Crime Scene Midterm

Non- Optical Physical Properties of Glass

-these sorts of comparisons are most useful in proving the two pieces CANNOT be associated - when sheet glass is rolled, the rollers leave parallel striation marks (ream marks) - thickness can be measured accurately • however thickness is not constant especially in curved pieces of glass • thickness is very useful in proving that 2 pieces of glass are not from the same source

glass subject to 3 types of forces

1. compressive force- squeezes the material 2. tensile force- expands the material 3. shear force- slides one part of the material in one direction and another part in a different direction

The 3 Important characteristic of fingerprints

1. fingerprints are unique. No two people have the exact same set of characteristics. 2. fingerprints do not change over time 3. fingerprints patterns can be classified and those classifications are then used to narrow the range of suspects

to examine glass, 2 samples are needed

1. glass from crime scene 2. glass fragments belonging to the suspect then compare samples by color, fracture pattern, striations, etc..

properties of substances can be grouped into 2 main categories

1. physical 2. chemical

Choke

A device placed on the end of shotgun barrel to change the dispersion of pellets.

Individual characteristic

A feature that is unique to one specific item.

Questioned sample

A sample of unknown origin

Explainable differences

A sound scientific explanation for any differences between the evidence and the reference material

Triangulation method

A technique used to record measurements for crime scene sketches, measuring the location of the evidence (X,Y) from fixed points (A,B)

Cartridge

Ammunition enclosed in a cylindrical casing containing an explosive charge and a bullet, which is fired from a rifle or handgun.

Smokeless powder

An explosive charge composed of nitrocellulose or nitrocellulose and nitroglycerin.

Nitroglycerin

An explosive chemical compound obtained by reacting glycerol with nitric acid. Nitroglycerin is used in the manufacture of gunpowder and dynamite.

Reticle

An eyepiece containing a grid of fine lines that is placed on a magnifying glass to determine the position of the letters being examined.

Primer

An igniter that is used to initiate the burning of gunpowder.

Tool mark

Any impression, scratch, gouge, cut, or abrasion on an object that is the result of a tool forcibly coming into contact with the object.

Physical evidence

Any object that can establish that a crime has been committed or can link a crime and its victim or its perpetrator.

Cortex

Consists of an orderly array of spindle-shaped cortical cells, which is aligned parallel to the length of the hair. Contains pigment bodies which contain melanin (a natural dye) and cortical fusi (irregular-shaped air spaces of varying sizes)

Medulla

Consists of one or more rows of dark colored cells that run lengthwise through the center of the shaft. Can either be cylindrical (human) or patterned (animal). Each pattern is specific to the particular species from which that hair came

Striations

Fine scratches left on bullets, formed from contact of the bullet with imperfections inside the gun barrel.

Fingerprint development

Fingerprints start forming when a fetus is in the 9th or 10th week of development and those fingerprints become permanently fixed by the 17th week of gestation

Francis Galton

In 1892 he published "Fingerprints," and in it the first classification system for fingerprints. Prints can be identified with minutia.

Evidence

Information about a crime that meets the state or federal rules of evidence

Typed and Word-Processed Documents

Investigation of documents typed on type-writers is still taught to future document examiners Typewriters have many individual characteristics Examination of a word-processed document may not establish enough individual characteristics Two types of printers—inkjet and laser Document examiner is more likely to be able to link a particular document with a laser printer than an inkjet printer due to blurring on the edges of letters in an inkjet printer

layers (horizons) of soil

O horizon- uppermost; heavily decomposed organic matter; microorganisms, insects, worms A horizon- topsoil; dark in color; mostly humus (decayed plants and animals) B horizon- subsoil; lighter colored; humus poor C horizon- fragmented bedrock and clay

Water-based and oil-based paints are composed of three major ingredients:

Pigment - either organic or inorganic; provides color * Solvent - the liquid in which the pigment, binder, and other ingredients are suspended * Binder - a material that polymerizes and hardens as the paint dries, forming a continuous film that holds the paint to the painted surface

Hair Morphology

Primarily composed of keratin (a strong protein that is resistant to chemical decomposition and can retain its structural features for a long time)

Magnaflux method

Restores information placed on iron or steel. First, the examiner must pretreat the weapon by grinding the material down until it is smooth. Then a magnet is applied to back side of the gun. The examiner will coat the surface with oil and then add metal shavings. The metal shaving will arrange themselves to show the shadows of the previous numbers.

Federal Rules of Evidence (FRE)

Rules that govern the admissibility of evidence into federal court.

Collecting Hair Evidence

Should be collected by hand, using a bright light to illuminate the area being searched. Can be collected using a wide, transparent sticky tape, lint roller, or a special evidence vacuum cleaner. Strands should be individually packaged in paper packets. If collected on tape, the entire lint roller or sticky tape should be packaged in a polyethylene storage bag

Edward Henry

Student who brought it to the police force in 1901 and in 10 yrs his system was used through the English speaking world.

FBI Fingerprints

The FBI has the largest collection on fingerprint records in the world, including fingerprints from more than 64 million people.

external ballistics

The events that occur after the bullet leaves the barrel of the gun but before it strikes its target. They tell well the perpetrator was when he/she fired the bullet. The bullet may travel a straight path or it could have ricocheted as result of impact with another job. If a ricochet bullet was the cause of death it may exonerate the suspect.

internal ballistics

The events that transpire within the firearm. Includes the striking of the firing pin, the scratching of the sides of the bullet by rifling, and any other imperfections on the inside of the bullet made by the gun barrel.

Bore

The interior of a gun barrel.

Identification

The process of matching a set of qualities or characteristics that uniquely identifies an object

Lands

The raised section of a rifled barrel.

Rifling

The spiral grooves on the inside surface of a gun barrel that make the bullet spin.

Gauge

The unit used to designate size of a shotgun barrel. The interior diameter of a shotgun barrel is determined by the number of lead balls that fit exactly in the barrel and are equivalent to 1 lb. For example, a 16-gauge shotgun would have a bore diameter of a lead ball that is 1/16 lb.

Acid Etching method

Used on firearms that are iron or aluminum. First, the area is ground smoothly. For iron, a liquid called Fry's reagent is applied to the area. The damaged metal is eaten away thus revealing the serial numbers. For aluminum alloys they use a mixture called Vinella's reagent. If the weapon contains silicon then the Hume-Rothery solution is used. The acid may continue eating the metal, so it is important to properly document the serial numbers when they are exposed.

Forgery

When a person creates or alters an existing object in an attempt to deceive other individuals, whether for profit or for other nefarious purposes, such as entering the country illegally.

Locard's exchange principle

Whenever two objects come into contact with one another, there is exchange of materials between them.

density gradient column

a glass tube filled (from bottom to top) with liquids of sequentially lighter densities -sample placed in tubes-> components fall through layers-> distributions compared -all samples collected should be packaged individually - paper envelopes or glass containers should not be used -forensic geologist looks for unusual- uncommon mineral, microfossil, human made material

weight

a measure of the force of attraction of the earth for an object - weight varies with location

Electrostatic detection apparatus

an instrument that uses electrostatic charge as the mechanism to visualize paper fiber disturbances

Fiber

any long, thin, solid object * Has a high aspect ratio * Most fibers of forensic interest are very common and are encountered daily in homes and workplaces * Most fibers do not undergo physical, biological, or chemical degradation while at a crime scene

sand

coarse particles

soda-lime glass

commonly used in most windows and bottles

concentric cracks

cracks that appear as an imperfect circle around the point of fracture

tangential cracks

cracks that appear as an imperfect circle around the point of fracture • grow from one radial crack to another and from the loaded side to the unloaded side

radial cracks

cracks that radiate in many directions away from the point of fracture • grow from the load point outward and from the unloaded side to the loaded side

organic soil

decayed remains of palnts

Individualization

demonstrates that an object is unique, even among members of the same class, or that two separate objects were at one time a single object

Forensic Characteristics of Soils

forensic soil analysis is a comparative technique - more than 1000 different soil colors -important that soil be dried in an oven before comparison (wet- changes color) - soil color has been standardized- Munsell soil color notation - soils often are passed through sieves to separate soil components by size -when separation is complete, fractional weight of each screen is determined then compared

Latent fingerprint

friction ridge impression not visible to the naked eye. Caused by the transfer of body perspiration or oils.

Plastic fingerprint

friction ridge impression that is left on a soft surface. Ex. Wet paint or clay

Patent fingerprint or visible fingerprint

is a friction ridge impression that is visible to the naked eye. Ex bloody finger print

Glass

is solid with an amorphous structure

7 base units of measurement

length mass time electric current thermodynamic temperature amount of substance luminous intensity

Known sample

material that comes from a proven or known source

Modus operandi

method of operation (MO)

algor mortis

natural drop in body temperature that occurs after death

Silver Nitrate

only used after iodine and Ninhydrin have been tried. Silver nitrate reacts with the salt and can then be seen under ultra violet light.

reference standard

physical evidence whose origin is known and that can be compared to evidence collected at a crime scene

Iodine Fuming

place iodine crystals and the latent print in a container which is then headed and the sublime iodine reacts with the body oils. But a picture must be quickly taken because the print will fade after the heating stops.

Transfer evidence

produced by contact between person(s) or object(s), or between person(s) and person(s)

Ninhydrin

reacts with the amino acid in fingerprints to produce a dark purple color called Ruhemann's purple

terminal ballistics

refers to what happens when the bullet strikes the target. When bullet strikes a target it is called an entry wound. If the caliber of the bullet is large enough it can travel through one victim and into another victim.

inorganic soil

remnants of rock fragments

4 major methods of commercial printing

screen printing, letterpress printing, lithography, and intaglio

mineral

solid inorganic substance that occurs naturally -more than 2000 minerals, forensic geologist encounter about 50 minerals - "signature"- combination of minerals and human made components in soil

projectile

the load of a bullet shot at a pane of glass

entrance side

the loaded side of a projectile

Super Glue fuming

the moistures and salts present in the fingerprint cause the super glue fumes to polymerize into a solid.

postmortem interval

time elapsed since death

laminated glass

two sheets of glass bonded together with a plastic sheet between them • automobile windshields are made from this

goals in examining glass evidence

• to determine the broader class to which the glass belongs, thereby linking one piece of glass with another • to individualize the glass to one source- a particularly difficult challenge given that glass is so common in modern society

Automobile paint

Several different layers of paint are applied during manufacturing * Electrocoat primer (black or gray in color) * Primer surfacer * Basecoat (the car's actual color) * Clearcoat (resistant to scratches, solar radiation, and acid rain) * A careful analysis that reveals the layer structure will allow an examiner to individualize the paint chip

Tracing

The copying of a genuine signature by placing the desired signature on top of a piece of paper over and tracing over it so that an indentation is made on the paper.

3 layers of hair

The cuticle (outer layer) * The cortex (middle layer) * The medulla (innermost layer)

Grooves

The cutout section of rifled barrel.

Extractor

The device that extracts the spent cartridge from the gun's chamber.

Caliber

The diameter of the bore of a firearms (other than a shotgun). Caliber is usually expressed in hundredths of an inch or in millimeters.

Indented Writing

The impression left by the pen on a second sheet of paper below the page that contained the original writing

Ejector

The mechanism in a semiautomatic weapon that ejects the spent cartridge from the gun after firing.

Breechblock

The metal block at the back end of a gun barrel.

Point of convergence

The most likely point of origin of the blood that produced the bloodstains

Black powder

The oldest gunpowder, which was composed of a mixture of potassium nitrate (saltpeter), charcoal, and sulfur.

Characteristics of Traced Signatures

Unnatural pen lifts Retouching Shaking handwriting Blunt end strokes Two identical signatures

Comparison and Identification of Synthetic Fibers

Using a comparison microscope, examine the fibers for color, diameter, cross-section shape, pitting or striations, and the presence of dulling agents * Advantages of using a comparison microscope: * Does not destroy the fiber * Not limited by the sample size * Every forensic lab has one readily available

Transfer bloodstain

a bloodstain deposited on a surface as a result of direct contact with an object with wet blood on it (e.g. blood on a hand towel from wiping a knife)

chemical properties

a characteristic of a substance that describes how it reacts with another substance - gasoline burns

Soil

a complex mixture of inorganic and organic materials

mass

a measure of the quantity of matter - mass does not vary with location, person has the same mass on the moon as on earth - mass determined by weighing it on a balance

physical properties

a property that can be measured without changing the composition of the substance - color, odor, taste, hardness, density, etc

extensive physical properties

a property that is dependent on the amount of material present - mass, volume, length

intensive physical properties

a property that is independent of the amount of material present - ice to water; solid to liquid

Mohs scale

a scale that measures the hardness of minerals and other solids - 1 being the softest, 10 being the hardest - Mohs scale reflects their scratching power (an unknown substance's hardness is determined by using it to scratch minerals with a known scale - most glass is between 5 and 6 on the Mohs scale

crystalline solid

a solid in which the atoms are arranged in a regular order

amorphous solid

a solid in which the atoms have a random, disordered arrangement

baseline method

a technique used to record measurements for crime scene sketches that draws a line between the fixed points (A, B) and measures the distance to the evidence (X, Y) at a right angle from this line

Polar coordinate method

a technique used to record measurements for crime scene sketches, using a transit or a compass to measure the angle from the north and the distance to the evidence (X). This method is most commonly used in a large area crime scene (outside or in a warehouse) when a wall or side of a building is used to establish the fixed points (A,B).

Glass softens over...

a wide temperature range rather than melting sharply at a well defined temp

elasticity

ability of a material to return to its previous shape after a force is exerted on it -if a force exceeds the glass's elasticity, the glass fractures

friable

easily broken into small particles or dust

silt

finer particles

clay

finest particles

tempered glass

glass that has been heat treated to give it strength • also known as safety glass is 4X stronger than window glass • stronger because wind pressure or impact must first overcome the compression before there is any possibility of fracture • breaks into "dices"- small pieces without sharp edges. it is used in the side and rear windows of automobiles

fracture match

the alignment of the edges of two or more pieces of glass, indicating that at one time the pieces were part of one sheet of glass

Intaglio

the printing method used for security printing, such as for currency, passports and identity documents, is a printing method in which a metal printing plate is engraved, producing a raised image of the document

rib marks

the set curved lines that are visible on the edges of broken glass • it is best to examine the rib marks if a hole was made by a low speed projectile -bullet sequence of impacts- the first shot causes subsequent shots' fractures to "run out" wherever the original shots have been -if the size of the fragments of glass are too small, measurements of density and refractive index are used

international system of units (SI)

the system of measurement (metric units) used by most scientists -SI updated version of metric system; based on decimal system - standard unit of length= meter - standard unit of mass= kilogram

exit side

the unloaded side of a projectile • the exit hole is wider than the entrance hole

Henry Faulds

worked in a hospital and found that fingerprints would return to the exact same pattern after suffering a superficial injury In 1870 he began to classify fingerprint patters using loops and whorls

Early fingerprints

• Chinese used finger prints to sign documents more than 3000 years ago • But the first practical application of fingerprints was used in 1858 • William Herschel used them to prevent forgery in India • And all prisoners in jail • Found that the prints never changed

Fingerprints on Hard and nonabsorbent surfaces

• Ex: mirror, glass, tile, and painted wood. • Black or gray powder- applied with a camel hair brush • Magnetic powder - powder is spread over the surface with a Magna Brush. • Florescent powder- viewed under ultra violet light

Fingerprint statistics

• Galton calculated that the odds of two peoples fingerprints being the same are 1 in 64 billion. • However a positive fingerprint match is determined if two prints exhibit 12 of the same minute characteristics

Aspects of fingerprint patterns

• Most of the skin on your body is smooth however, skin on your fingers, palms, toes and soles are not. • They have tiny raised lines called friction ridges that allow you to hold onto things. • These lines form ridges (hills) or grooves (valleys) • Also you have small sweat pores which transfer sweat onto the surfaces

cracks will grow in 2 directions

• grow from the unloaded to the loaded side • radiate outward, away from the load point

5 types of microscopes are typically used for forensic examinations

* Compound microscope * Comparison microscope - used to compare to specimens * Stereoscopic microscope - most commonly used in crime labs * Polarizing microscope - helps with identifying minerals * Microspectrophotometer - combines the capability of a spectrophotometer and a microscope

When hair evidence is found, it's important for the examiner to answer two questions:

* Is the hair human? * Does it match the hair of the suspect?

Nitrocellulose

A cotton-like material produced when cellulose is treated with sulfuric acid and nitric acid; also known as "guncotton." Nitrocellulose is used in the manufacture of explosives.

Search warrant

A court order allowing law enforcement officers to search a suspect's home or business and take specific items as evidence

arrest warrant

A court order, signed by a judge, that authorizes the arrest of a particular person.

finished sketch

A drawing made by a professional that shows the crime scene in proper perspective and that can be presented in court.

Semiautomatic pistol

A firearm that fires and reloads itself.

Collection and preservation of firearms

A first responder primary job, when recovering a weapon, is to render it safe.They must also do everything possible to preserve evidence: magazines, spent cases, ammo, fingerprints.Everything collected must be preserved with an evidence tag that contains a full description. Must also keep the chain of custody intact.

Freehand method

A forger practices making the signature until he/she is able to create a reasonably similar signature.

chain of custody

A list that records every official person who handles a piece of evidence. Those in the chain put their initials and the date on the evidence container.

Secondary crime scenes

A location other than the primary crime scene, but that is in some way related to the crime, where evidence is found

Microscopes

A microscope has at least two lenses: an objective lens and an ocular lens (or eyepiece)

Rough sketch

A rudimentary first sketch created at the crime scene with care for accuracy in depicting dimensions and locations but no concern for aesthetic appearance.

Questioned Document

A term used to describe any object that contains typewritten or handwritten evidence information but has yet to be proven authentic. Includes checks, contracts, driver's licenses, passports, Social Security cards, etc.

Trace Evidence

A term used to describe small, often microscopic, objects that are readily transferred between people and places. **Can include: hair, fibers, glass, soil, feathers, pollen, dust, and paint

Broach cutter

A tool that is pushed through the gun barrel to form the rifling.

3 Basic Types of Handwriting

Block: uppercase unjoined letters Cursive: lowercase letters that are joined together Script: lowercase unjoined letters

Hair used as evidence

Can only be used for definite identification if the hair has a tag attached that can be analyzed for DNA. Hair does not have a sufficient number of unique characteristics to be positively associated with a particular person to the exclusion of all others

Destructive tests

Chemical analysis

Forensic Analysis of Paint

Comparison of the paint chip in question and the paint chip from a known source * Color is the most important forensic characteristic (considering that there are thousands of paint colors) * Each layer of paint's color, odor, texture, and thickness should be recorded * Infrared beams can identify major organic components present in the paint chip (when compared with the infrared spectra of known organic materials * A stereomicroscope (SEM) can be used to identify the inorganic pigments in a paint sample and can give more detail to the layer structure * Large paint chips can undergo destructive chemical tests for additional data * The application of a solvent will cause swelling or the generation of colors à may help identify resins and pigments in the chip * By comparing the reaction of the questioned and known samples to different solvents, the examiner can determine if the two came from a common source

Cuticle

Consists of scales of keratinized tissue that overlie the cortex. The scales have a unique shape and pattern depending on which animal species they came from

Reference Hairs

Control (reference) samples should be collected from the victim, the suspect, and any other individuals who could have left hair at the crime scene * Reference hairs should be taken from all pertinent regions of the body * 50 head hairs (from different regions of the head) should be plucked * In sexual assault cases, 24 pubic hairs also should be plucked or cut close to the root

Integrated Ballistics Identification System (IBIS)

Correlates and matches both fired bullets and discharged cartridge cases. a pair of high speed computers are connected using the National Ballistic Information Network. The computers cross reference matches from the examiner's sample to existing samples on file. The heart of the system is the digital image recognition software called Bulletproof. Bulletproof stores images as a set of binary numbers and compares the set of numbers against others. When matches are found, examiners look through a microscope to compare the samples.

Natural Fibers

Derived from plant or animal sources, include materials such as cotton, flax, silk, wool, and kapok * In most textile materials, the natural fibers are twisted or spun together to form threads

Ricochet

Deviation of a bullet's trajectory because of collision with another object

Nondestructive tests of paper

Differences in dimensions Micrometer to measure thickness Light source to view watermark

Fingerprints on soft or absorbent surfaces

EX: Cloth, Paper, and Cardboard • Iodine Fuming • Ninhydrin • Silver Nitrate • Super Glue fuming

Serial Number Restoration

Every gun has a serial number stamped into the frame. Some weapons have the number in multiple location. Federally licensed dealers must keep records of the serial numbers and name of persons who purchased weapons from them. Police use these records to establish suspects, and whether or not the gun has been reported stolen.

Ballistic testing

If the weapon is located, firearms examiners will conduct test firings in order to determine if bullets match. This is done by firing into a block of gel or a water tank. Water tank test slow the bullet without damaging it, so the examiners can get an ideal known sample. If the same gun is fired with the same ammunition then the results will remain constant.

The Magnifying Glass

Magnify images by refracting (bending) light rays as they repeatedly pass through the air and back through the lens. *The magnified image is called the virtual image

Collection and preservation of ammunition

Marking must be preserved, each cartridge should be labeled and be put in separate envelopes, only rubber utensils should be used.

Wadding

Material placed between the propellant and the projectile; it is used in shotgun shells and muzzle-loader firearms to distribute force on the projectile.

Collection of Paint Evidence

Most likely to be found in crimes involving burglary or involving a vehicle * It's important to keep the paint chip intact; it's best not to try to remove paint that is smeared on clothing or other objects (its should be packaged) * A reference sample must be collected for comparison (from an undamaged area) * In a crime involving a car, collect a paint sample from as close to the point of impact as possible (not all surfaces of a car fade at the same rate and some parts may have been repainted) Also the investigator must remove ALL layers of paint, down to the metal * In burglary cases, tools used by the burglar may have trace paint attached and should be packaged * An investigator must be very careful when handling paint chips à a physical "jigsaw" match of a questioned paint chip and an area where the reference paint is being collected is conclusive evidence

Passive blood stain

Patterns created from the force of gravity only.

Photocopied Documents

Photocopiers use the same technology that is used in laser printers. Document examiners may be able to tell the manufacturer and model of a photocopier from the photocopied document by looking at marks left on the paper.

Fourth Amendment

Protects Americans against unreasonable searches and seizures. No soldier, Gov agent, or police can search your home without a search warrant.

Synthetic Fibers

Rayon (the fist human-made fiber) was introduced in the US in 1901 * Modern manufactured fibers are classified into two categories: * Cellulosic fibers - produced from cellulose-containing raw materials (trees or other plants) * Synthetic fibers - produced from chemicals made from refined petroleum or natural gas

Exemplar

Representative item to what evidence can be compared