Review Questions ch 4-7 Forensics

What aspect of a fingerprint determines its individuality?

The individuality of a fingerprint is determined by careful study of its ridge characteristics (minutiae) - ridge endings, bifurcations, enclosures, and other ridge details, which must match two fingerprints in order for their common origin to be established

What is a flow pattern? What should one surmise if a flow found on an object or body does not appear consistent with the direction of gravity?

Flow pattern - a bloodstain pattern formed by the movement of small or large amounts of blood as a result of gravity's pull. If a flow found on an object or body does not appear to be consistent with the direction of gravity, one may surmise that the object or body was moved after the blood had dried.

Distinguish between a homicide and a suicide.

Homicide - Non accidental death resulting from grossly negligent, reckless, or intentional actions of another person. Suicide - Must be demonstrated that the individual carried out act alone. Multiple gunshots might lead one to suspect homicide, however a person who is committed to ending their life may take several shots if the wounds are not instantly fatal.

Explain how the infrared microspectrophotometer determines the identity of a specimen. What type of physical evidence is the microspectrophotometer typically used to analyze?

Infrared - examine fibers and paints - obtaining such a spectrum allows the analyst to better identify and compare the type of chemicals from which these materials are manufactured.

How did the comparison microscope make possible modern firearms examination?

Its ability to give the firearms examiner a side-by-side magnified view of bullets. Bullets that are fired through the same rifle barrel display comparable rifle markings.

List and describe the three types of fingerprints that may be found at a crime scene.

Latent/invisible - impressions caused by the transfer of body perspiration or oils present on finger ridges to the surface of an object. Visible - a fingerprint made when the finger deposits a visible material such as ink, dirt, or blood onto the surface Plastic - a fingerprint impressed in a soft surface (putty, wax, soap, dust)

What is the difference between real image and virtual images?

Real image - an image formed by the actual convergence of light rays on a screen Virtual image - an image that cannot be seen directly. It can be seen only by a viewer looking through a lens.

Describe what's entailed in an internal examination during an autopsy.

Removal of all organs through a Y-shaped incision beginning at the top of each shoulder, and extending down to the pubic bone. Weighing, dissecting and section each organ of the body. Microscopic examination can help in determining the cause of death. Special care taken to identify pre-existing conditions that could've caused death.

How can pools of blood aid in reconstructing a crime scene?

Small and large pools of blood can be helpful in reconstruction because they can be analyzed to estimate the amount of time that has elapsed since the blood was deposited. Can yield information about the timing of the event.

Which of the following is of paramount importance in the interpretation of bloodstain patterns: A. Direction of Impact B. Surface Texture C. Angle of impact D. Amount of Blood

Surface texture is of paramount importance in the interpretation of bloodstain patterns - harder and nonporous surfaces result in less spatter, rough surfaces result in irregularly shaped stains

Describe the characteristics of a blunt force injury.

caused by a nonsharpened object (bat, pipe). Can abrade/scrape tissue. May cause lacerations(skin splitting and tearing)/contusions(bruise). .

Describe the characteristics of a sharp force injury.

occur from weapons with sharp edges (knives, blades). Capable of cutting or stabbing. Cut (longer than deep). Stab (deeper than length). Blood may be found at different locations throughout the scene.

List items to be collected and sent to the forensic laboratory from an autopsy.

- Victim's clothing - Fingernail scrapings or clippings - Combings from head and pubic areas - Buccal swab (for DNA typing purposes) - Vaginal, anal, and oral swabs (sex related crimes) - Bullets recovered from the body - Swabs of body areas, such as breasts or penis, suspected of being in contact with DNA arising from touching or saliva - Hand swabs from shooting victims (for gunshot residue analysis)

Describe important factors in characterizing a gunshot wound.

-Estimated range of fire (appearance of the wound can help in estimating how far the firearm discharged) -Powder residue distribution around the wound to make estimates -Contact shots - fired against the body - not accident -Wound track - following track of projectile through body.

List the five categories of the manner of death.

-Homicide - Non accidental death resulting from grossly negligent, reckless, or intentional actions of another person. -Suicide - Result of an individual taking his or her own life with lethal intention. -Accidental - Must not be intent to cause harm through gross negligence on the part of a perpetrator or the victim -Natural - Disease, continual environmental abuse. Chronic drug and alcohol abuse, longtime exposure to natural toxins or asbestos. -Undetermined - Rational classification cannot be established. Cause of death cannot be determined.

What is the difference between the shape of a bloodstain that impacts a surface at a low angle and one that impacts at a higher angle?

A drop deposited at a 90 degree angle of impact will be approx. circular in shape with no tail or buildup. As the angle deviates from 90, the stain becomes elongated in shape. Buildup will occur when angles are larger, whereas longer tails will appear as the angle becomes smaller.

Describe livor mortis.

A medical condition that occurs after death and results in the settling of blood in areas of the body closest to the ground.

Describe the phenomenon of rigor mortis.

A medical condition that occurs after death and results in the stiffening of muscle mass. The rigidity of the body begins within 24 hours of death and disappears within 36 hours of death.

When should a fingerprint be "lifted" from a crime scene? Describe how to lift and preserve a fingerprint using adhesive tape.

A print should be "lifted" from a crime scene when it is on a large, immovable object. One method of lifting is to dust the print with fingerprint powder, then cover the print with adhesive tape. When the tape is pulled up, the powder is transferred to the tape. Then the tape is placed on a card that provides a good background contrast with the powder.

After death the body undergoes a process known as algor mortis. What is this?

A process that occurs after death in which the body temperature continually cools until it reaches the ambient or room temperature.

What is a void pattern? How might a void pattern be useful to investigators?

A void is an area within a deposited spatter pattern that is clear of spatter, caused by an object or person blocking the area at the time of the spatter's deposition. The blank space on the surface or object can give a clue to the size and shape of the missing object or person. They can also help to establish the body position of the victim or assailant at the time of the incident.

How can an investigator tell the direction of travel of blood from the shape of a bloodstain?

An investigator may discern the direction of travel of blood that struck an object by studying the stain's shape. As a stain becomes more elliptical, its direction becomes more discernible because the pointed end of a bloodstain faces its direction of travel. The distorted end of an elongated stain indicates its direction of travel.

In general, as both the force and velocity of impact increase, what happens to the diameter of the resulting blood droplets?

As both force and velocity of impact increase, the diameter of the resulting blood drops decreases.

How can a scanning electron microscope be used to determine whether a suspect has recently fired a gun?

Attempt is made to remove any gunshot particles that remain on a shooter's hand with a piece of adhesive tape. Examine under SEM for presence of particles that may have originated from the bullet primer. Characterized by their shape, size, and elemental composition. Through the use of this technique, the elements lead, antimony, and barium are frequently found in most primers and can be rapidly detected and identified.

Describe what's entailed in an external examination during an autopsy.

Broad overview of the condition of the body and the clothing. Obvious damage to clothing should be matched to injuries on the body. General characteristics of the body (gender, age, hair, etc). Presence of tattoos, scars, puncture/track marks. Mouth, nose and ears examined. Fingernails examined/scrapings. Classifying injuries, examined injuries include abrasions, contusions, lacerations, and sharp-injury wounds. Attention to genitalia, esp. in cases of sexual abuse. X-rays.

What important considerations must be made when determining PMI using forensic entomology?

By determining the most developed stage of fly found on the body, entomologists can approx. the postmortem interval (time elapsed since death). Newly emerged flies are important forensic interest, as they indicate that an entire blowfly cycle has been completed on the decomposing body. -Affected by environmental influences (geographic location, climate, weather conditions, presence of drugs) cold temperatures hinder the development of fly eggs into adult flies.

What determines the size of blood drops in a cast-off pattern?

Cast-off: a bloodstain pattern that is created when blood is flung from a blood-bearing object in motion onto a surface. The size of the drops are directly related to the size of the point from which they were propelled.

What is digital imaging and how is it used in fingerprint analysis? What is the greatest limitation to digital imaging?

Digital imaging - a process through which a picture is converted into a series of square electronic dots known as pixels; the picture is manipulated by computer software that changes the numerical value of each pixel. The main limitation of digital imaging is that it is only as useful as the images it has to work with. If the images are poor or incomplete, enhancement procedures will not work.

What is the drawback effect? How is it helpful to an investigator?

Depending on the distance from the victim at which the gun was discharged, some back spatter may strike the gunman and enter the gun muzzle. Blood within the muzzle of a gun can "place" the weapon in the vicinity of the gunshot wound.

Describe the approach for estimating the time of death by measuring potassium levels in the ocular fluid.

Determine potassium levels in the decedent's ocular fluid - the fluid within the eye (AKA Vitreous humor). Draw a clean, bloodless sample from one eye with syringe as soon as possible at the scene, then draw a second sample from the other eye an hour or two later. Can determine the rate at which potassium is released into the vitreous humor and use it to approximate time of death. Also dependent on ambient temperatures.

What is the dermal papillae and why is it important in fingerprinting?

Determines the form and pattern of the ridges on the surface of the skin.

What is expirated blood? Name two ways to distinguish expirated blood from other types of bloodstains.

Expirated blood patterns - a pattern created by blood that is expelled out of the nose, mouth or respiratory system as a result of air pressure and/or airflow. The presence of bubbles of oxygen in the drying drops can differentiate a pattern created by expirated blood, it also may be lighter in color than impact spatter as a result of being diluted by saliva.

What is the difference between forward spatter and back spatter? Which is more likely to be deposited on the object or person creating the impact?

Forward spatter is blood that travels away from the source in the same direction as the force that caused the spatter. Back spatter is blood directed back toward the source of the force that cause the spatter. Back spatter is more likely to be deposited on the object or person who was creating the impact.

Name and describe two methods for documenting bloodstain patterns.

Grid method - setting up a grid of squares of known dimensions over the entire pattern using string and stakes. All overall, medium-range, and close-up photographs are taken with and without the grid. Perimeter ruler method - involves setting up a rectangular border of rulers around the pattern. The large rulers show scale in the overall and medium-range photos, whereas the small rulers can be inserted to show scale in the close-up photos.

Why might investigators overlook some high-velocity spatter?

High-velocity spatter is created by a force traveling at 100 feet per second or faster and producing drops with diameters less than 1 mm. The drops are very small, and may not travel far. They may fall to the floor or ground, where investigative personnel could overlook them.

Define the terms area of convergence and area of origin and explain what kind of information each reveals to an investigator.

Impact spatter patterns can offer investigators clues about the origin of the blood spatter and the position of the victim at the time of impact. Area of convergence - the area on a 2D plane where lines traced through the long axis of several individual bloodstains meet; this approximates the 2D place from which the bloodstains were projected. Area of origin - the location in 3D space from which blood that produced a bloodstain originated; the location of the area of convergence and the angle of impact for each bloodstain is used to approx. this area.

Who published the first book on the science of fingerprinting?

In 1892, Francis Galton published Finger Prints

Define the cause of death.

Identifies the injury or disease that led to the chain of events resulting in death.

Describe each of the three classes of fingerprints. Which class is the most common in the population? Which is least common?

Loops - a class of fingerprints characterized by ridge lines that enter from one side of the pattern and curve around to exit from the same side of the pattern. Whorl - a class of fingerprints that includes ridge patterns that are generally rounded or circular in shape and have two deltas Arch - a class of fingerprints characterized by ridge lines that enter the print from one side and flow out the other side

List two types of specialized fingerprint powders and name one advantage each has over traditional fingerprint powder.

Magnetic-sensitive powder - spread over a surface with a magnet in the form of a magna brush (does not have bristles to come in contact with the surface so there is less chance that the print will be destroyed). Comes in black and gray and works on items such as finished leather and rough plastics, where the texture of the surface tends to hold particles of ordinary powder. Fluorescent powder - fluoresce under UV light. by photographing under this light, it is possible t o avoid having the surface color obscure the print. BOTH FOR LATENT PRINTS

Why might an examiner choose a microscope with a lesser magnification to study a specimen?

Maximum useful magnification - 1,000x NA of the objective. Any effort to increase magnification would result in no additional detail - "empty magnification" Considerations: -Size of specimen area or field of view. As magnifying power increases, field of view decreases. Start low and increase.

What is the basic difference between a scanning electron microscope and the other microscopes used in the crime laboratory?

Microscopes - use light coming off the specimen to produce a magnified image. Scanning electron microscope - image is formed by aiming a beam of electrons onto the specimen and studying electron emissions on a closed TV circuit. goes through a process. emitted electrons are then converted into an image of the specimen for display on the cathode-ray tube. High magnification, high resolution, great depth of focus.

How does one calculate the magnification power of a compound microscope?

Total magnification equal to the product of the magnifying power of the objective and eyepiece lenses.

What is the most commonly used chemical method to visualize latent fingerprints on porous materials? If this method is unsuccessful, what other technique typically is used?

Ninhydrin - a chemical reagent used to develop latent fingerprints on porous materials by reacting with amino acids in perspiration - is the chemical method of choice due to its extreme sensitivity and ease of application. When this fails - physical developer - a silver nitrate-based reagent formulated to develop latent fingerprints on porous surfaces.

What does numerical aperture (N.A.) measure? What is the difference between a lens with N.A. 1.0 and one with N.A. 0.5?

Numerical aperture - the ability of an objective lens to resolve details into separate images instead of one blurred image is directly proportional to the NA value of the objective lens. NA 1.0 can separate details at half the distance of NA 0.5

Why does a compound microscope produce greater magnification than a magnifying glass? How does the eyepiece lens contribute to magnification?

Ordinary magnifying glass can acheive a magnification of about 5-10 times. Higher magnifying power = compound microscope. Constructed of two lenses mounted at each end of a hollow tube. Eyepiece works like a magnifying glass and further magnifies this image into a virtual image.

List two unique characteristics of the stereoscopic microscope.

Presents a distinctive 3D image of an object Magnifying powers from 10x to 125x. The stereoscopic microscope is more convenient because of the prisms in its light path that permit the formation of a right-side-up image. -Wide view and great depth of focus -large working distance that enables it to examine big, bulky items

What aspect of a fingerprint forms the basis for primary classification under the FBI system? What is the main drawback of the FBI system?

Primary classification - the presence or absence of the whorl pattern is the basis for determination of the primary classification. Assigned 16 for the first finger, and half for each following finger. Any finger with arch or loop pattern is assigned a zero. Drawback - a fingerprint classification system cannot identify an individual by itself, it merely provides the fingerprint examiner with a number of candidates, all of whom have an indistinguishable set of prints in the systems file.

What is the most widely used microscope in the crime laboratory? What features make it particularly suited for examination of physical evidence?

Stereoscopic microscope - wide field of view and great depth of focus. large working distance that enables it to examine big, bulky items characterize physical evidence as diverse as paint, soil, gunpowder residues, marijuana

What major advance in fingerprint technology was pioneered by Juan Vucetich and Sir Richard Henry? What was the importance of this advance?

The creation of classification systems capable of filing thousands of prints in a logical and searchable sequence in 1891. Sir Henry proposed his in 1897. Both are still used today in Spanish (Vecetich) and English speaking (Henry) countries to file fingerprints

What is the final step in fingerprint identification? Why is this step necessary if a computerized database of fingerprints is available to the forensic scientist?

The final step in fingerprint identification is always visual comparison of the prints in question by a trained examiner. A computer database can only produce a list of prints that are similar to the print in question; it cannot make a positive identification.

How does the first transfer pattern in a series differ from subsequent ones?

The first transfer pattern will be dark and heavy with blood, whereas subsequent transfers will be increasingly lighter in color. The transfers get lighter as less and less blood is deposited from the transferring object's surface.

Name three factors that affect the amount of backward spatter produced by a gunshot wound.

The location of the injury, the size of the wound created, and the distance between the victim and the muzzle of the weapon all affect the amount of back spatter that occurs.

What is crime scene reconstruction?

The method used to support a likely sequence of events at a crime scene by the observation and evaluation of physical evidence and statements made by individuals involved with the incident

What phenomenon underlies many of the new chemical techniques used to visualize latent fingerprints? Why is this phenomenon so valuable in fingerprint visualization?

The phenomenon of fluorescence serves as the underlying principle of many of the new chemical techniques used to visualize latent fingerprints. Substances that emit light or fluoresce are more readily seen either with the naked eye or through photography as compared to non-light-emitting materials. Thus, techniques based on fluorescence permit better visualization of all prints and allow the visualization of faint prints that other methods may fail to visualize.

List the areas of the skeleton that can be used to determine the gender of skeletal remains.

The sex of the decedent can be determined by the size and shape of various skeletal features, esp. those of the pelvis and skull. -Female pelvic bones tend to form a wider more circular opening than that in a male pelvis because of woman's child-bearing capabilities. -The female sacrum (flat bone above the tailbone_ is wider and shorter than a males (equal). -The angle formed at the bottom of the pelvis is a right angle for females, but acute in males. -Male skulls are larger in size than females. Male skull tends to have more pronounced brow bone and mastoid process (bony protrusion behind jaw)

Explain how the shape of stains in a trail pattern can help investigators determine the direction and speed at which a person was moving.

The shape of the stains in a drip trail pattern can help investigators determine the direction and speed at which a person was moving. The tails of drops in a trail pattern point in the direction the person was moving, and more circular stains are found where the person was moving slowly. May be helpful in reconstruction.

What is a transfer pattern? How is a simple transfer pattern created?

Transfer pattern - a bloodstain pattern created when a surface that carries wet blood comes in contact with a second surface; recognizable imprints of all or a portion of the original surface or the direction of movement may be observed. Simple transfer patterns are produced when the bloody object makes contact with a surface and the object is removed without any further movement.

How do comparison microscopes work and when is it used.

Two compound microscopes combined into one unit. Circular field equally divided into two parts. Used for side-by-side comparison of specimens. Compare bullets, cartidges, and other opaque objects, hairs, fibers.

Briefly describe how the Automated Fingerprint Identification System (AFIS) creates a fingerprint image. What characteristics of the fingerprint does the AFIS record for comparison?

Uses automatic scanning devices that convert the image of a fingerprint into digital minutiae that contain data showing ridges at their points of termination(ridge endings) and the branching of ridges into two ridges (bifurcation). Relative position and orientation of the minutiae are also determined, allowing the computer to store each fingerprint in the form of a digitally recorded geometric pattern.

What is the main advantage of the microspectrophotometer?

a forensic analyst can now view a particle under a microscope while a beam of light is directed at the particle in order to obtain its absorption spectrum. - provide the forensic scientist with added information that will characterize trace quantities of evidence.

Why is it almost impossible to obscure one's fingerprints by surgery or mutilation?

such a wound would have to penetrate 1-2 mm beneath the skins surface. It would be totally impossible to obliterate all the ridge characteristics, and the presence of permanent scars provides new characteristics for comparison.

How does a magnifying glass enlarge objects viewed through it?

the magnifying glass makes things appear larger than they are because of the way light rays are refracted, or bent, in the passing from the air into the glass and back into the air.

What is vertical illumination and under what conditions would a forensic scientist use it to examine a sample? Why is it superior to transmitted illumination under such conditions?

vertical/reflected illumination - illumination of a specimen from above; in microscopy it is used to examine opaque specimens. (not transparent). the light source must be placed above the specimen so that it can reflect off the specimen's surface and into the lens system of the microscope.

How can a scanning electron microscope be used to identify the elements present in a specimen?

x-rays are generated when the electron beam of the SEM strikes a target. When SEM is coupled to a x-ray analyzer, the emitted x-rays can be sorted according to energy values and used to build a picture of the elemental distribution of a specimen. Because each element emits x-rays of characteristic energy values, the x-ray analyzer can identify elements present. Element's concentration can be determined by measuring the intensity of the x-ray emissions.