Forensic Evidence- unit 2-book notes

CASTING IMPRESSIONS WITH PLASTER OF PARIS

1. Preparation of the impression 2. Mixing the plaster 3. Pouring the plaster mix into the impression Allow to air-dry thoroughly for twenty-four to forty-eight hours or longer if necessary. No attempt should be made to remove soil or to clean the casts, because this action will most likely destroy the impression. Also, the soil adhering to the casts may be used by the laboratory analyst as a comparison standard for any soil found on the suspect's shoes. Each cast should be loosely and individually wrapped in paper or a paper bag (do not wrap or place in plastic). Package the wrapped cast in a cardboard box and tape seal. The cast should then be wrapped in shock absorbent or porous packaging material that does not exclude air if the casts need to be shipped or mailed.

Edmond Locard is credited with recognizing the theory of exchange. He stated very accurately that every contact leaves a trace. Also referred to as Locard's theory of exchange, the concept supports the following three statements:

1. Traces of the victim and the scene will be carried away by the perpetrator. 2. Traces of the perpetrator will remain on the victim, and the victim may leave traces of himself or herself on the perpetrator. 3. Traces of the perpetrator will be left at the scene. Any item can and may be physical evidence that a crime has occurred. Trace evidence can provide valuable leads for investigators, but first it must be recognized as evidence by the CSI. Even if the trace evidence cannot be positively identified as having originated from a sole source to the exclusion of all others, it can still corroborate other types of evidence and create linkages between the suspect to the crime or to the victim, to a specific item, or link the victim to the scene.

If the suspect vehicle cannot be conveniently moved, the test impressions must be made at the scene. The following procedures should be used:

1. Use a smooth, flat surface such as smooth concrete. 2. Put 12-inch-wide strip of poster board in front of each tire in order to record the entire circumference, which can be at least 6 feet, so be sure to have poster board or acetate film that long to allow for the entire rotation of the tire. Mark the top of the tire with chalk so that when the tire is rolled, you will know that a complete rotation occurred. Coat the poster board with fingerprint ink. 3. Do not drive the vehicle but rather have the car in neutral and while one person sits in the driver's seat, have others pushing the vehicle slowly. Roll the vehicle over the inked poster board, and then replace the inked poster board with clean poster board strip or acetate film. I like using acetate because the rolled impressions can be rolled up and placed in a tube. These acetate rolls can then be used to overlay the actual impression from the crime scene. Always ask your firearms lab personnel what they prefer. 4. Roll the inked tire(s) over the clean poster board to produce a test impression. 5. Label all "test boards" properly for identification and sequencing before re-covering the boards. Roll each individual tire and mark each test tire with its proper location and information on the vehicle (e.g., front driver's side).

The methods to be employed at the crime scene described in this text are based on a selection of those techniques that are readily utilized at the crime scene, as opposed to those methods that are better performed in the laboratory or that can be accomplished only in the laboratory because of equipment, personnel, and safety considerations. The following sequences of procedures for each surface type at the scene will help to optimize the recovery of useful latent impressions. The best approach to latent processing for all surface/latent deposit combinations should follow this sequence:

1. Visual examination followed by laser/alternate light/ultraviolet light search. The search for latent prints should begin with those methods that are nondestructive and that preserve the latent prints, patent prints, and other types of physical evidence that may be present at the scene (particularly trace evidence) and that may be lost or destroyed by latent processing. The first step in the examination for fingerprint impressions is a visual examination of the suspect surfaces, using adequate lighting for the presence of visible impressions and other types of physical evidence that may be destroyed by fingerprint processing. This search should be augmented with high-intensity lighting, laser illumination, or alternate light sources, which may reveal impressions or trace evidence not seen without the illumination (many fibers will fluoresce under these lights). 2. Photographs of all patent prints and other evidence in the impressions prior to removal or tape lifting. Any patent impressions found in this preliminary search should be photographed prior to further treatment. Indented prints should be collected for processing in the laboratory when feasible. If it is not feasible to transport the impression-bearing object to the laboratory, then the crime scene technician/analyst must process the impressions at the scene. The impressions should be photographed with oblique (side) lighting and a cast prepared from silicone casting material in the case of indented patent impressions. Patent impressions in blood are treated with the methods for bloody prints. 3. Processing with physical or chemical methods. The choice of methods for latent print processing of the scene is a function of the surfaces to be processed for latent prints, the chemical nature of the deposit, and the environmental history of the impression. The crime scene technician/analyst should choose the method or the sequence of methods that has the most promise for the detection and collection of latent prints from each surface processed. In the sections to follow, the appropriate techniques for the various surfaces and composition of the latent deposit will be described. The analyst needs to be familiar with the best choice of method for each type of surface, combined with a consideration of the nature of the latent impression's composition. In addition, the history of the object bearing the impression plays an important role in the determination of which techniques and their sequence are likely the best choice, since wetting or exposure to moisture may destroy the water-soluble portions of the impressions, but has little effect on the water-insoluble portions of the impression (oils). The use of the wrong sequence of techniques may destroy any impression present and may prevent further treatment with other techniques. 4. Photographs of latent prints after development or visualization. It is a good practice to photograph the latent impressions after development at each step as a safety factor, particularly on those surfaces that may partially peel off or fragment, thus obscuring some or all of the impression. In addition, the photograph of the developed latent in situ is helpful during testimony, to illustrate the location and condition of the latent prior to lifting with tape. 5. Sketches of the location and orientation of the latent impression on the lift card or in the investigator's notes. The documentation of the location and orientation of the latent impressions detected will provide details for any reconstruction efforts for testing statements by a suspect with regard to innocent placement of the latent impressions if your agency requires this.

The initial procedures at the crime scene for all surface/latent deposit combinations (both nonabsorbent surfaces and absorbent surfaces) should be the following: Steps 1 and 2 are assumed to have been completed before proceeding to the next step in the sequence for each surface type in the sections to follow. The suggested techniques for each of the following sections thus begin with step 3, with the assumption that steps 1 and 2 have been accomplished or given due consideration prior to proceeding to step 3 in the sequence for each surface/deposit combination to be processed.

1. Visual examination with adequate lighting, followed by laser/alternate light. The search for latent prints and other types of physical evidence present at the scene, particularly trace evidence that may be lost or destroyed by latent processing, should begin with a visual examination in good light, followed by examination with a laser light, an alternate light source, and an ultraviolet light. These methods are nondestructive, and they are prudent precautions against the loss of latent prints or trace evidence that may be lost by premature processing for latent impressions with physical or chemical techniques. 2. Photographs of all patent prints, developed latent prints, and other evidence in the impressions prior to removal or tape lifting. It is strongly recommended that developed or visualized impressions be photographed prior to collection or lifting attempts, so that in the event the impression is not successfully recovered, a permanent record of the impression is available. The visualized impressions should be photographed at each stage of the sequence as they are developed, since the impressions developed at an early stage may be superior to those developed at a later stage in the sequence. 3. Selection of the physical and/or chemical process or sequence in the following sections based on surface type, nature of the latent deposit, and its environmental history. 4. Photographs of developed prints as processing proceeds. 5. Documentation of recovered latent prints in notes and sketches.

rough, nonporous surfaces usually cannot be processed with latent fingerprint powders. Most of these surfaces will require chemical processing to develop latent impressions. The chemical method used depends on the particular surface type of the object suspected of containing latent prints. For most wet, nonporous surfaces, dry the surface and then treat as for dry surfaces, or use small particle reagent.

3. Cyanoacrylate fuming. Cyanoacrylate fuming may be better than powders on these surfaces. The use of dye-impregnated CA in the fuming wand may eliminate the need for postfuming dusting with luminescent powders. 4. Small particle reagent (especially for wet surfaces).

Of the methods of recording impressions available to the investigator, only casting can capture three-dimensional surfaces with the detail needed for comparison in the laboratory. As an additional benefit, trace evidence may adhere to the surface of the casting material. In this respect, casting often collects evidence that would otherwise go unpreserved (e.g., soil on a plaster cast of a footprint). Inspect the impression for sticks, stones, and leaves that have fallen loosely into the impression after it was made. Carefully pick out such debris with tweezers. Any debris that was pressed into the soil with the impression should not be disturbed but rather left in the impression, since removal may disturb the impression. Small amounts of standing water may be removed with a small eyedropper. When preparing a cast using plaster of paris, it is advisable to place a dam around the impression to be casted. The dam can be constructed of materials such as tree branches, wood slats, paint stirrers, etc., but the use of commercially prepared casting frames (see Figure 9-12) is simpler and more efficient. When preparing a cast using dental stone, it is normally not necessary to use a dam or casting frame, but the practice is not discouraged.

Casting Materials for Footwear and Tire Impressions The methods of casting are very simple and require only practice and following instructions for the preparation of the casting medium. The two materials used widely for casting of footwear and tire impressions are plaster of paris and dental stone. Dental stone may produce finer detail than plaster of paris and is generally a stronger material once it is set. Either method will produce casts of sufficient quality for laboratory comparisons. The crime scene investigator will need to be proficient in the use of the particular method chosen prior to any attempt to cast impressions in a case. Instructions are given here for plaster of paris casting. For casting with dental stone, the investigator should follow carefully the instructions for the particular dental casting stone material acquired for casting impressions. Hilderbrand prepared a table with instructions for preparing a cast based on the conditions of the medium in which the impression was produced (see Table 9-1).3 The media covered in the table includes wet soil, mud, dry soil, sand, and water-covered and snow impressions.

DNA Probative Value Not every item at a crime scene should be considered probative evidence. The facts of the case, along with other information, will assist in making the determination of what evidence should be tested in the lab. The best evidence occurs when DNA belonging to the victim or suspect is found where it is not supposed to be (see Box 6.2). Many laboratories use a triage system. They will accept only a certain number of items from each case in a single submission. They want to examine the most probative items first. Therefore, it is very important for the CSI to be in contact with the laboratory. If the first round of items does not yield any probative evidence, the lab will often accept additional items. DNA is a very stable molecule and can remain intact for many years. Maintaining the integrity of the crime scene and preventing contamination of physical evidence recovered at the scene or on the victim are essential to the credibility of the CSI and the subsequent lab analyses

DNA analysis can ■ Identify a suspect. ■ Implicate or eliminate a suspect. ■ Place a known individual at a crime scene. ■ Refute a claim of self-defense. ■ Put a weapon in a suspect's hand. ■ Change a suspect's story from an alibi to one of consent. ■ Analyze unidentified remains. ■ Resolve paternity/maternity cases. ■ Link related cases. ■ Provide leads in cold or unsolved cases. ■ Be used to appeal convictions.

Impressions in Snow

Forensic products are available that can assist in the preservation of snow impressions; however, you can also use dental stone to cast these types of prints. Never cover snow impressions with plastic; this could cause them to melt or degrade, making it impossible to preserve the original evidence. After taking initial photographs, make sure the impressions are visible in the photographs by lightly spraying gray primer paint into the impression to highlight the ridges and grooves. Do not hold the can too close to the impression because the compressed air may disturb fragile ridges, tread marks, or shoeprints. Dental stone can be used with a potassium sulfate additive that speeds up the setting time and allows the casting to set in extremely cold conditions. Another commercially available product, Snow Print Waxs, is a wax that can be sprayed on the impression and allowed to set up for 10 minutes prior to using regular dental stone mixed with cold water (see Figure 5.26). Either method can yield good-quality impressions if the impressions are allowed to dry for approximately 1 hour prior to the CSI trying to lift them. Additional time—up to 48 hours—should be allocated for the entire cast to dry in a temperature-controlled environment

Glass Comparison Standards

Glass Standards from Windowpanes Collect as much as possible of the broken glass for the comparison standard. If size limitations preclude collecting all the glass, always attempt to obtain a sample from an area near the point of impact. Collect window glass standards from the frame, not the ground, as it is possible for glass on the ground to be from another source. Always keep the comparison samples separate from the questioned fragments. Place in separate containers, and label accurately. Glass Standards from Bottles Collect as much as possible of the bottle fragments. Occasionally, it is necessary to reconstruct the bottle or to develop latent fingerprints on the surface. The more fragments collected, the better the chance of obtaining latent prints from the bottle surface. Glass Standards from Automobile Headlights Glass from automobile headlights may be needed to compare with glass fragments in an accident victim's clothing or to identify the make of vehicle involved. Collect as many fragments as feasible from the roadway. If the vehicle is located, collect the entire headlight remaining in the lamp housing.

Collection at the Scene .

Hairs Visible and Firmly Attached to an Inanimate Object Photograph the hairs in place (if feasible). Leave hairs intact on the object. Diagram and note the exact location and the number of hairs adhering to each object. Package the object so that the hairs cannot become dislodged in transit. Label the object and its package, and transport it to the laboratory. Hairs Visible But Not Firmly Attached to an Object Photograph the hair before collection (if feasible). Sketch and note the location of the hairs and the number of hairs present. Then carefully remove the hairs with disposable or clean pair of forceps, or gloved hand, and package them. Place the hairs in small pill boxes, glass vials, or other tightly capped containers. Hairs may also be placed in folded paper bindles (see Figure 6-2), and then packaged in an envelope. Label the packages with standard identification data, and reference the collection in the field notes

When you are preparing clothing or other items such as bed linens for air-drying and submission, crime laboratories recommend the following steps to protect the integrity of the evidence:

If air-drying articles, place them on or over a piece of clean paper. If any debris or trace evidence falls from an item while it is drying, it will be collected on the paper—which should also be folded and submitted with each individual article. ■ Guard against cross-contamination. Do not allow stained areas to rub against or contact each other or another unstained area. Place several clean sheets of paper on the work surface and then lay the article of clothing on top. Use paper or thin cardboard as a barrier to separate the layers of clothing. Insert paper inside sleeves, pants legs, between the front and back of a shirt or jacket, and inside a dress. Fold the item loosely or roll it up using the sheets of paper on the workspace as the outer protective layer. Seal the rolled-up item with tape and place each one into a separate paper bag. Record all case-identifying information on the bag and apply biohazard warning labels to the outside of each package. ■ Physical evidence can be contaminated by the CSI's sweat or saliva drops (sneeze or cough). Be sure to use proper PPE when processing the scene and packaging physical evidence. ■ Laundering of clothes or bed linens does not always remove all traces of bodily fluids. Collect and submit these items for laboratory analysis because forensic biologists can utilize specific techniques to detect unseen trace evidence.

Any items bearing toolmarks removed as evidence should be clearly marked with case number, initials, and date of removal. The evidence should also be marked to show the inside or outside, top or bottom, and the surface with the toolmark. If the object bearing the toolmark is instead removed, a sufficiently large piece of the surrounding surface area should be included to prevent damage to the mark through bending, splintering, or breaking. Any small removable item such as a doorknob, latch plate, or lock should be marked by the investigator showing the top and front of the item as it was positioned before removal. Use an indelible felt tip pen, or include a separate drawing with the submitted evidence. Many objects bearing toolmarks that are detached on forced entry can be submitted directly, including segments of window or door molding, window or doorsill, latches, bolts, locks, or doorknobs. Where doorknobs are twisted, note whether anything obstructs access to the knob from either side (posts, door setback). If the mark appears on items too large to be sent to the laboratory, prepare a cast of the toolmark using Mikrosil™ or other silicone casting compound.

If an actual item cannot be submitted for toolmark examination, a toolmark cast can be made. A suitable casting material is Mikrosil™. This two-part substance reproduces the very fine detail needed for the microscopic comparison. Two speeds of hardener are supplied in the casting kit. The slow hardener is suitable for normal casting. The fast hardener is used for casting in very cold climates. Complete mixing of the casting material and hardener is essential. A properly mixed portion will be workable for about one to two minutes, and the cast can be removed in about ten minutes. Since a hardened Mikrosil™ cast cannot be permanently marked with a pen, the cast must be placed in a suitable container that can be appropriately marked with item number, location, date, and name of the person making the cast (STD ID data). Figure 9-16 illustrates a Mikrosil™ casting kit consisting of the cast base material and the hardener

Inked Impressions

If suspect footwear is located, inked impressions of the shoes should be made by rolling ink on the bottom of the shoes, stepping inside the shoes, and walking on clean, white paper, Mylars, or gel lifters (see Figure 5.23). If the impression to be compared was a bare footprint, the same techniques should be used for obtaining friction ridge details on the bottom of the foot. First, clean the feet and then apply printer's ink with a fingerprint roller. Direct the subject to take several steps on clean white paper, carefully documenting the time and location where you secured the comparison footprints. The suspect and the CSI should both sign the papers on which the inked impressions are collected. Another method for obtaining footwear, footprints, fingerprints, palmprints, or tire prints uses common household supplies. Spray a nonstick cooking spray on the item to be printed; then step or roll the items on the paper or a Mylar sheet to create the impressions. Next, apply fingerprint powder to develop the ridge, shoe, or tire details. This procedure works well for agencies that have a limited budget; a can of nonstick cooking spray can always be purchased and kept in the crime scene response vehicles

Precautions for Evidence Hairs Before attempting the specific collection procedures in the following list, note these precautions.

Package Individual Hairs in an Individual Container Single hairs should be packaged in a paper bindle, glassine envelope, or vial, and then packaged in a paper envelope. Both the bindle/glassine envelope/vial and the paper envelope should be marked with standard identification data. Do Not Package Wet Evidence Hairs or objects containing hair evidence should be airdried before placing in appropriate containers. Biological materials degrade with time. This process is accelerated when wet items are sealed in airtight containers such as plastic bags. Do not use a fan or blow dryer to dry the hairs or objects as they may result in loss of the hairs. Place Exhibits Only on a Clean, Paper-Covered Flat Surface Do not place exhibits directly on a tabletop. The work area, such as a table, should be covered with new paper before placing the exhibits on the surface. Avoid cross-contamination between all evidence and control samples by handling the exhibits one at a time, and by always using the Clean Technique (changing gloves and disposable or thoroughly cleaning tools between handling of each evidentiary item). Label Each Evidence Container with Standard Identification Data Each container should have the following minimum data: submitter's initials, case number, item number, source, and date. Document the chain of custody

The preferred method of sample collection is in this order: (1) pulled hairs, (2) backcombed hairs, and (3) cut (near the skin) hairs. It is not essential to have pulled hairs for standards provided that the hairs collected are cut very close to the skin, but the laboratory prefers hair specimens collected in the order indicated, because the growth phase of the hair may be a consideration in the examinations (the growth phase is determined by examination of the root).

Scalp hair standards should also be collected from other individuals related to the case who may have been the source of any evidence hairs collected. Members of the household where hair evidence is recovered or other individuals who frequent the residence should be requested to provide hair standards for elimination purposes. This precaution may save considerable time in the laboratory and also may account for any hairs that do not match either the victim or the suspect. This step may be important in those cases in which mistaken identity is claimed as a defense by eliminating unknown sources for those hairs not matching a suspect or a victim. Combed Hair Specimens New (unused) plastic combs should be used to collect loose hair from all parts of the scalp. Combs should be used for only one subject and packaged with the hair sample. Back comb the scalp hair briskly. Catch falling hairs on a large sheet of paper, fold into a bindle, and place bindle and comb into an envelope. Seal and label appropriately. The combing of the subject's scalp will help collect any foreign hairs present and will also provide a specimen of the hairs that are ready to fall from the scalp. Pulled or Cut Scalp Hair Standards The sample of hair standards should be representative of the entire scalp and should include samples from the front, the left side, the right side, the crown area, and the back of the scalp (see Figure 6-3 for sampling sites). At least fifteen to twenty hairs from each area should be submitted for a total of seventy-five to one hundred hairs. Collect about fifty hairs in total by collecting approximately ten hairs each from the top left, top right, top center, middle left, and middle right of the pubic region (see Figure 6-4). It is preferred to collect pulled hairs, but hairs cut as close to the skin as possible may be adequate for the laboratory examinations and comparisons. Check with your local laboratory first

An arson investigation is a complex endeavor that requires a well-trained and experienced arson investigator to be in charge of the investigation. Arson investigators use several important considerations in determining whether the cause of a fire is accidental or intentional. The arson investigator is trained in the interpretation of the "burn pattern" of a fire, which will indicate whether or not an accelerant (often called "added flammable") was used to start and spread the fire. The investigator will also seek to eliminate accidental causes of the fire, such as faulty wiring or materials on a stove that were left unattended. The presence of an identified accelerant in the burn areas is an important factor in the arson investigator's determination that an arson has been committed. Thus, the investigator will make every effort to locate and collect accelerant residues for laboratory analysis in order to assist in establishing that a crime occurred. The specific type of accelerant used can then be compared with standard samples seized from a suspect in order to link the suspect to the arson. The role of the crime scene investigator in arson scene investigations is typically to assist the arson investigator in the documentation and collection of physical evidence at the scene. In some instances, the crime scene investigator may be a competent, certified arson investigator, in which case, he or she also acts as the arson investigator, analyzing the scene for evidence of arson and also collecting the physical evidence samples necessary to assist in the determination of arson or fire from natural causes. In this instance, additional crime scene investigators will assist the arson investigator in documenting the scene and collection of the physical evidence

The term "volatile" refers to that attribute of a liquid that permits the liquid to evaporate rapidly, thus forming a gas above the surface of the liquid. Some liquids are very volatile but not flammable, such as chloroform, whereas others may be both volatile and flammable, such as gasoline. The most common term applied to volatile flammables used in arson fires is "accelerant." Volatile flammables used to commit an arson are referred to as "accelerants" because they accelerate the fire, resulting in its rapid spread and destruction of the structure involved. Examples of volatile flammables often used as accelerants in arson cases are gasoline, kerosene, lighter fluid, and white gasoline. The process of combustion requires three elements for its propagation: heat, oxygen, and fuel, commonly referred to as the "fire triangle." Fire will be extinguished when any one of these three elements is absent. Fire does not burn solids or liquids (in general), but instead burns the gases formed above them. Heat acts to vaporize the liquid or solid, converting it into a gas that then combines with oxygen to "burn" above the liquid pool. Thus, when flammable liquids soak into material or run into "cracks" there will be insufficient oxygen to support combustion. In these cases, residues of the flammable substance can be collected by collecting the material into which the liquid has soaked. The process of the chemical reaction that occurs during the fire was added to the fire triangle in 2011, so the fire triangle is currently referred to as the "fire tetrahedron" (four-sided figure, see Figure 6-15). n. Arson "sets" or items suspected of being part of an arson set, such as matches or matchbooks, should be collected and submitted along with the accelerant evidence. One common "igniter" found at arson scenes is a match used to ignite the fire. Figure 6-16 illustrates a partially burned match collected at an arson scene compared to a matchbook from the suspect. The igniter match is shown fitting into the matchbook (left top), a fracture match, and the comparison of the inclusions in the match to those of the adjacent match (right top) remaining in the matchbook seized from the suspect

Photographic Techniques

To locate footwear or other impression evidence at the indoor crime scene, darken the area and use a strong white light at an oblique angle. Alternate forensic light sources can also provide illumination that may assist the CSI in locating impression evidence more effectively than by just using a flashlight. Document the location of each impression and photograph each one individually to provide an accurate representation of the crime scene. Remember that this type of documentation may be useful for substantiating or invalidating victim/suspect statements later in the investigation. Because lifting or preserving all impressions may not be possible, you should always photograph each one individually. A photograph or lift provides a two-dimensional reproduction of the print. Be sure the photographs accurately depict the location of the impression evidence in relation to the overall crime scene

What Laboratory Examinations Can Reveal

Whether the Hair is Animal or Human If the hair is an animal hair, the analyst may be able to determine the species of animal from which the hair originated. The Body Type of the Hair Virtually all forensic human hair comparisons involve either scalp or pubic hairs. Very few data are available regarding the conclusions that can be drawn from the examination of other body hairs. Investigative Leads Investigative leads from hair evidence include the color, length, and form (straight, wavy, curly, highly curled) of the hair(s) present as evidence. These factors may allow the investigator to infer the hair color, length, and form of the suspect's hair. In addition, the hair form may permit the possible inference of the suspect's racial group (African, Asian*, European) and possibly the gender of the suspect (although longer hair is commonly seen in males as well as females). If visible flesh is adhering to the root(s) of the hair(s), the investigator may conclude that the hair was forcibly removed from its source. Whether the Hair "Matches" a Suspected Source If the Hair Does Not Match a Suspected Source The Hair Comparison Is Inconclusive DNA in Hair

As mentioned before, the selection of methods for use at the crime scene depends on a number of factors. Of the techniques available to the crime scene investigator, the following are suitable for routine use at the scene: (1) laser light and alternate light sources; (2) development with brush and the various latent fingerprint powders; (3) cyanoacrylate (superglue) fuming (especially with portable cartridge-based fuming wands); (4) small particle reagent; (5) iodine fuming; and, in some instances, (6) ninhydrin or its analogues or substitutes such as DFO. These methods are sufficiently portable and cost-efficient to be considered for routine use in the field. The use of other methods will be restricted by the availability of specialist personnel, budget constraints, and safety factors. Laser lights, alternate lights, and ultraviolet light examination may be used to reveal latent fingerprints on nonabsorbent or absorbent surfaces. Chemical powders may be used to enhance the fluorescence of the latent prints for both visualization and photography. The fluorescence in latent prints is due to certain natural constituents in the sebaceous secretions and any contaminants present that fluoresce under laser light. The advantage of these special light examinations is that they are nondestructive and may be used prior to any other development method as a rapid screening device, in addition to their ability to produce identifiable impressions for photography. Fingerprints on smooth, nonporous surfaces such as glass, paint, glossy plastics, and other polished surfaces can usually be developed with latent powders (graphic/ carbon based). The fingerprint brush should be clean and free from oils or other materials that may affect the efficiency of dusting with the brush. Latent fingerprint brushes cannot be used after getting wet. It is always a good idea to have more than one latent brush in your latent fingerprint kit. The brush should be swirled vigorously to remove excess powder, and then dipped lightly into the powder with a swirling action, lifted, and swirled again, and then applied lightly to the surface in a circular manner. Once the latent becomes visible, the print should be dusted lightly in the direction of the ridges until clearly visible. It is important to avoid overdusting, since the print may be wiped clean by too much dusting. If overdusting (overprocessing) occurs, the crime scene technician can do what is called a second lift. Lift the first overdusted impression, and then if enough oil or other material in the latent fingerprint is still present, the crime scene technician can lightly apply more powder to this latent print, and then if this second impression is present, label it as a second lift. This tells the latent examiner that the same latent fingerprint has been lifted twice rather than there being two fingerprints lifted. The print is then lifted with fingerprint tape and placed on a latent fingerprint card designed for this purpose. The card should be labeled immediately. Some agencies may require that a sketch placed on the card illustrating the location and orientation of the print be also done. Labeling the latent cards (on the back) on the scene prevents them from becoming mixed up before labeling, avoiding any potential confusion as to which print came from which object. Practice dusting many objects with varying surfaces to gain insight into the proper amount of dusting necessary for quality development of the latent prints before attempting the processing of a crime scene. The fingerprint tape should be rubbed sufficiently to remove any air bubbles present. The edge of roll of latent tape or an eraser can help with the elimination of air bubbles. If the tape cannot be removed without destroying the print, then the tape is left on the surface and the object collected. If the tape can be removed, the tape should be pulled up from the end away from the tape roll, and the tape should then be transferred to a latent card. Crime scene technicians tear tape and do not use knives to do so. A triangle is created at the end of the tape to ensure that the technicians do not touch the sticky side of the tape thereby contaminating or adding their own prints to these sections There are a number of approaches to the use of cyanoacrylate fuming for latent print development. The fuming can be accomplished by placing the items to be processed in a fuming chamber (or a more inexpensive container is a plastic bin with an air tight lid), and then fuming with any of a number of commercially available kits or with kits prepared by the crime scene technician/analyst. Fuming chambers are also available commercially or can be constructed by the crime scene technician/analyst. The investigator should refer to the commercial suppliers of crime scene equipment and supplies for availability of such equipment and supplies. Of particular interest is the development of the superglue fuming wand for cyanoacrylate fuming. This technique should allow for effortless fuming in the field by investigators. The cyanoacrylate cartridges can also be ordered with dye added to the cyanoacrylate, which can be visualized with fluorescent lighting, thus eliminating the additional step of treating the fumed impressions with a fluorescent dye. Fuming wands are available from most crime scene products distributors

he use of a large, widemouthed (about 8 ounces or larger) plastic jar (see Figure 5-4) for the working supply of fingerprint powder is suggested for several reasons. First, an amount of powder approximately one-half-inch deep should be placed in the jar. If the powder becomes contaminated during use, the small amount of powder can be discarded, and the jar rapidly cleaned and refilled with new powder. However, companies now offer one-time use for powders and disposable fingerprint brushes to prevent contamination from occurring. Second, this large-sized jar allows the fiberglass brush to be stored in the open jar between successive lifts, so that the brush does not have to be set down on a surface. Third, the size of the jar allows the analyst to dip the brush lightly into the powder and to swirl the head to apply powder to the brush. Fourth, the excess powder can be removed by swirling the brush in the jar above the powder layer, thus avoiding contaminating the scene or the analyst's clothing with the powder. These jars, which are very inexpensive, are particularly suitable for the patrol officer's latent print kit.

Labeling of Suspected Accelerant Residues Collect specimens from different areas for each suspected arson set, placing each specimen in a separate labeled container. Do not overlook other types of physical evidence that may be present: fingerprints, shoe prints, broken glass, toolmarks, or other types of evidence that may serve to identify the perpetrator or establish the act of arson. Label each container with the following minimum data:

• Location where the sample was collected. (Provide an exact description of where the sample was found or obtained. Sketches and photographs are of considerable help in this endeavor.) • Date and time of collection. • Name of suspect and/or victim (if known). • Department case numbers (fire and police departments). • Name (last, first initial) of evidence collector.

Firearms evidence often plays a crucial role in the reconstruction of events at the crime scene, particularly homicide crime scenes. A large percentage of homicides is committed through the use of firearms, and these crimes frequently require a reconstruction in order to eliminate an accidental shooting or a suicide as the cause of the decedent's death. Those aspects of firearms evidence that are frequently significant are muzzle-to-target distances, the precise location of expended cartridges at the scene, bullet hole locations, trajectories and ricochets, identification of the firearm that fired each bullet, and the presence or absence of gunshot residues on the hands of suspected shooters. Shooting reconstructions frequently determine whether a shooting was accidental, a suicide, or an intentional homicide. The reconstruction is also a means to test the veracity of alleged witnesses to a shooting. In one of the author's cases, a witness claimed that the victim was standing against a wall when shot. Reconstruction of the incident proved that the shooting victim was a considerable distance from the wall and in close proximity to the shooter. information avalable from a shooting incident reconstruction:

• Muzzle-to-target distances. • Minimum number of participants in the incident. • Number and type(s) of firearms involved in the incident. • Direction of projectile paths taken during the shooting incident. • Location(s) of participants during the incident. • Sequence(s) of events during the shooting incident.

Latent fingerprints in blood can be developed or enhanced in one of two general ways: (1) staining with a protein dye such as Amido Black or (2) treating with bloodstain testing reagents (such as tetramethylbenzidine) that form colored compounds by reaction with the heme portion of hemoglobin. Since the bloodstain testing methods are about ten times as sensitive as the staining methods and may reveal "invisible" blood, it may be preferable to use the bloodstain testing methods for fingerprints in blood rather than one of the protein staining methods.19 Amido Black is preferred to Crystal Violet for the protein dye, since Crystal Violet is toxic and should be used only in the laboratory by qualified analysts or chemists with access to proper safety equipment. It is important that whatever fingerprint technique is utilized, other evidence is not destroyed (such as DNA). Elimination prints are inked fingerprints of those individuals who may have contributed to latent fingerprints at the scene. Ideally, the elimination prints can be taken at the scene with a portable fingerprint elimination kit (see Figure 5-13). These kits have all the supplies necessary for taking high-quality inked prints. If the investigator does not have an elimination kit available, the elimination prints can be prepared using a small "pocket" inking pad and the backs of latent cards as a substitute The importance of obtaining good quality, clear inked impressions of the fingers and palms cannot be overstressed, whether the prints are obtained with standard ink and fingerprint cards or through a scanner that captures the print image. A current set of inked fingerprints and palm prints of identified subject(s) should be forwarded to the Forensic Laboratory (ATTN: LATENT PRINT SECTION) when requesting a fingerprint comparison. Adherence to this procedure will ensure the following:

• That the submitting agency can provide a witness to establish that the inked fingerprints belong to the specific suspect(s) in question. • That an admissible court exhibit can be prepared, should this case go to the superior court or grand jury. • That the suspect(s) in the case is (are) the same individual(s) whose inked fingerprints are on file (quite often, because of the large number of prints on file, different individuals may have the same names, dates of birth [DOBs], and physical descriptions). • That inked prints submitted for comparisons are: • Properly inked and fully rolled. • Accompanied by the full name and description of the subject for comparison. • Dated and signed by the individual in the submitting agency who rolled the prints and can testify, in court, as to the origin of the fingerprints. • Sent to the attention of the latent print analyst currently assigned to the case if previous work on the case has been done.

A forensic odontologist can examine and evaluate bitemarks to a reasonable degree of dental certainty. Four findings can be related to the examination of bitemarks provided a suspect has been identified:

■ Definite—To the exclusion of all others (i.e., only the suspect could have made the bitemark impression) ■ Consistent—No features present that will exclude the suspect ■ Possible—Due to the nature of the injury, positive confirmation or exclusion of the suspect is not possible ■ Exclusionary—Definitely not made by the suspect

FINGERPRINTS AS PHYSICAL EVIDENCE There are four common types of fingerprints:

■ Visible—These prints are usually made when the friction ridges are coated with a substance that is transferred to another surface—such as fingerprint powder. ■ Plastic—These prints are impressions left in a soft material, such as soap or wax. ■ Latent—These prints are hidden or invisible to the naked eye. ■ Wet—These prints are made in liquids, such as blood. Once fingerprints are located on an item of evidence, they must be photographed without a scale and by placing a scale in subsequent pictures before any other steps are taken to either preserve or process the prints. A scale is necessary for examiners to ensure a 1:1 ratio when comparing photographs to other impressions