Chapter 2 - Understanding The Nature Of Physical Evidence

Question 1

What is a class characteristic?

Answer 1

Traits or characteristics of evidence that allow the item to be compared with a group.

Class characteristics serve forensics best in eliminating possibilities.

Question 2

What are some examples of class characteristics?

Answer 2

Size, color, common manufacturing patterns, taxonomic classifications, etc.

Question 3

Describe the differences between class and individual characteristics of evidence.

Answer 3

Class characteristics are compared with a group, while individual characteristics are compared with a specific object or person.

Question 4

Of the available methods for DNA analysis, which is the best for individualization in forensic work and why?

Answer 4

Short tandem repeat (STR) because it combines concepts of PCR but created statistical discrimination that was higher than that developed through RFLP.

Question 5

Describe how tape is used to collect hair and fiber evidence at the crime scene.

Answer 5

Wide clear adhesive tape is cut in 8 to 10 inch lengths. Holding the two opposite edges, the technician applies the adhesive side of the tape to the surface in question and lightly applies pressure.
This single piece of tape is used to cover a specific area until it’s tackiness is reduced. It is then applied adhesive side down to a piece of transparent plastic and secured if necessary.

Question 6

When evaluating glass fractures for direction of force, which fragments can be used in the evaluation?

Answer 6

Directions of force determinations evaluate the radial fractures present in the first concentric ring in pane glass.

Question 7

How is paint layering used to different differentiate two paint samples, such as when comparing a paint sample from a hit-and-run to a suspect vehicle?

Answer 7

Looking at the number of layers for each primer, base, and clear coats.

Question 8

Comparison of soil sample is based on environmental variations from one sample to the next. What are some of the most significant forms of environmental variation?

Answer 8

Color, consistency, pollen, minerals, substances.

Question 9

How would evaluating crime scene evidence involving a pistol differ from that involving a revolver?

Answer 9

Pistols eject casings automatically, revolves do not.

Question 10

Rifling refers to what two manufactured components of a barrel?

Answer 10

Projections (lands) and depressions (groves).

Question 11

How are bullets marked for evidence and why?

Answer 11

These items should not be marked on directly, but individually packaged and labeled.

Question 12

Of the two methods used to collect tool mark evidence (collection of the entire item or casting of the mark), which is better and why?

Answer 12

The tool mark itself should be collected as evidence, as castings may not capture the microscopic level of detail.

Question 13

What is the most significant class characteristic in shoe mark examinations and why?

Answer 13

Tread design, because it can narrow down the search to a type and brand of shoe.

Question 14

What type of containers are used to collect fire scene evidence in which accelerants are believed to be present?

Answer 14

Fire scene evidence should be sealed in clean, unlined paint cans or glass jars.

Question 15

In terms of a forensic analysis, what is the difference between a forged writing and a traced writing?

Answer 15

Tracings are conscious efforts to copy a known writing and will lack fluid movement within the writing.

Question 16

What is the most appropriate response by the crime scene technician for collecting a computer for computer forensic analysis?

Answer 16

?

Question 17

What is Locard’s principle of Exchange?

Answer 17

Every contact leaves its trace.

Question 18

What is cross-contamination?

Answer 18

Is the inappropriate handling or exposure of evidence.

Question 19

Fingerprints are classified using what system?

Answer 19

A modified Henry system developed by Sir Edward Henry in India in 1894.

Question 20

What are the three basic Ridge patterns?

Answer 20

Loops (65%), whorls (30%), arches (5%).

Question 21

Fingerprints are identified and individualized based upon:

Answer 21

Finding agreement of individual characteristics, with no unexplainable dissimilarities.

Question 22

The majority of fingerprints found deposited in the crime scene consist of:

Answer 22

Approximately 98% water and 2% a combination of grease, oil, salts, and amino acids.

Question 23

What are the three basic forms of fingerprints?

Answer 23

Latent prints, patent prints, and plastic prints.

Question 24

What is a latent print?

Answer 24

Generally invisible prints created by the deposit of normal body secretions.

Question 24

What is a patent print?

Answer 24

Fingerprints caused by the deposit of contaminants( bloody or greasy finger marks) that are visible to the naked eye.

Question 25

What is a plastic prints?

Answer 25

Fingerprint Impressions where a print has been deposited in a soft surface such as wax.

Question 26

What is the RFLB technique in relation to DNA?

Answer 26

Restrictive fragment length polymorphism. It’s a way of mapping variable regions of the DNA molecule, allowing comparison of one DNA source with that of another.

Question 27

What is the PCR technique in relation to DNA?

Answer 27

Polymerase chain reaction. It allows scientists to copy the DNA structure in small samples, quantities too small to allow for RFLP techniques.

Question 28

What is STR technology in relation to DNA?

Answer 28

It is short tandem repeat technology. Both degraded and small samples could be examined to the point of individualization.

Question 29

In general the following are biological materials that have the potential to provide DNA profiles:

Answer 29

·Blood
·Bone
·Dandruff
·Hair when the root or scalp cells remain attached to the shaft
·Feces
·Fingernails and fingernail scrapings
·Finger prints
·particulate the flesh, skin, or organs
·nasal and ear secretions
·saliva
·semen
·sweat
·vaginal secretions

*urine has limiter potential to provide a DNA profile

Question 30

What is mDNA?

Answer 30

Mitochondrial DNA, which is inherited singularly from the mother.

Question 31

It has been suggested that __% of any transferred hairs or fibers are lost in the first _ hours following the contact.

Answer 31

90, 8

Question 32

Examination of glass from the crime scene is typically directed at one of three basic determinations:

Answer 32

·Glass type
·Direction of force
·Sequence of force

Question 33

The method of evaluating direction of force in glass is referred to as the 4R rule, which states:

Answer 33

Ridge lines on radial fractures are at right angles to the rear.

Question 34

What is a radial fracture in glass?

Answer 34

Radio fractures radiate out from a central point in the fracture.

Question 35

What are concentric fractures in glass?

Answer 35

Concentric fractures encircle the central area of the fracture at various distances.

Question 36

What are conchoidal fractures in glass?

Answer 36

Conchoidal fractures will be obvious in the edge of the glass fragment. These fracture lines will Iie parallel to one side of the glass, and on the opposite side they will lie at nearly a 90° angle.

Question 37

When collecting a soil sample, what is the minimum amount required and what container is it put in?

Answer 37

1/2 to 1 cup of material in a pint-sized paint can.

Question 38

GSR contains trace amounts of three primary elements:

Answer 38

Antimony, barium, and Lead.

Question 39

Evaluation of GSR is conducted using what instrument/equipment?

Answer 39

Scanning electron microscope (SEM). The SEM seeks unique fused particles they contain all three elements (antimony, barium, and lead). Research indicates that the three elements will occur together in a single particle only in gunshot residue.

Question 40

In regards to firearms, what is a cartridge?

Answer 40

A single and complete unfired unit of ammunition.

Question 41

In regards to firearms, what is a projectile?

Answer 41

Referred to as the bullet. Often described based upon their construction (full metal jacket, semi jacketed, hollow point, wad cutter).

Question 42

Cartridges are either ______ fired or ___ fired, depending upon the location of the primer mechanism.

Answer 42

Center, rim.

Question 43

Weapons are generally placed into three categories, what are they?

Answer 43

Handguns, rifles, and shotguns.

Question 44

What does rifling do to the barrel of a firearm?

Answer 44

Gives the projectile spin, which stabilizes the bullet in flight making it more accurate.

Question 45

Firearms by Design and operation create or share a number of class characteristics with the ammunition they utilize. What are some examples of these class characteristics?

Answer 45

Caliber of the weapon, the shape of the firing chamber, the location of the firing pin, shape of any extraction or ejecting mechanisms, and the number, size, and direction of twist present in the lands and grooves.

Question 46

The two most common tool marks on fired shell casings are the _____ ___ mark and ______ marks.

Answer 46

Firing pin, ejector.

Question 47

What are the three General categories of tool mark evidence?

Answer 47

Stration, compression, and saw and drill marks.

Question 48

What is a striation to mark?

Answer 48

A mark that is caused when the cutting edge of a tool is brought in contact with and slid against a target surface.

Example: scraping of a chisel along the door casing as it is forced into place.

Question 49

What is a compression tool mark?

Answer 49

Occurs when a tools forced into soft material.

Example: a hammer head against wood or gypsum board.

Question 50

In terms of tire marks, what is the wheelbase?

Answer 50

The wheelbase is the measurement of the width across the front or rear axle of the vehicle. Given a dual set of tire marks (both left and right side), track width is measured from either the outside tread to an opposite outside tread or from an inside trade to inside tread.

Question 51

What is wheelbase in terms of a vehicle?

Answer 51

Wheelbase is a measurement from the center of the front hub to the rear hub, the distance between the two axles.