Ch 4 Physical Evidence Flashcards
What is the greatest possibility of error when searching for weapons at a crime scene?
Ignoring common items of furniture or equipment at the scene as suspect weapons
The removal of spent bullets without damage to the original condition is an example of what?
Postmortem forensic science
Valuable evidence that typically gets recognized
Bloodstains on clothing and other objects
Blood splashes and and blood drops help to narrow ….
The size of the suspect group,
Support identity when a an sp is located,
And plot the movements of the v and the assailant
Relatively fresh bloodstains generally appear to be ….
Reddish-brown in color
The question that often must be answered of bloodstains?
Whether the stain is blood or some other substance
How is the determination of whether or not a stain is blood?
Preliminary test color, kastle-Meyer color test
This test is based on the reaction with enzymes in the blood which causes the test strip to turn a deep pink color
Kastle-Meyer color test
Theses test strips are a useful presumptive field test for blood
Hemastix
Test strips used with the Kastle-Meyer color test
Hemastix
Theses are a useful presumptive field test for blood
Hemastix
Drop sizes of blood increases with the
Distance of the fall
The tails or pointed ends on bloodstains indicate
The direction of movement
The round edges of blood stains face
The source of the bleeding
Another ? That must be answered is whether at one time blood was present at the crime scene…
And has since been cleaned up
Presumptive test that uses light rather than color as it reacts with blood
Luminol
Luminol helps identify whether blood at a scene…
Was cleaned up
Faint blue glow after spraying luminol
Luminescence
New trademark name that may be used in place of luminol
Bluestar
T/f
A room does not need to be darkened in order to use luminol
False
Advantage of bluestar over luminol
It’s reaction with a bloodstain can be observed without having to create complete darkness
Both of these presumptive tests are extremely sensitive and are capable of detecting bloodstains diluted up to 100,000 times
Blue star and luminol
Final determination in blood evidence
Whether it is human or animal origin
These tests are based on the reaction when animals, usually rabbits, are injected with human blood
Precipitin test
This test involves an injection that causes antibodies to form that react with human blood to neutralize its presence
Precipitin test
Another type if precipitin test is?
Gel diffusion
This test takes advantage of the fact that antibodies and antigens diffuse or move toward on another on a plate coated with a gel medium made rom polymer called agar
Gel diffusion
Gel medium made from a polymer
Agar
In gel diffusion , if a blood stain is human…
A line of precipitation forms where the antigens and antibodies meet
This type of test in determining whether blood is human is very sensitive and only requires a small amount of blood
Gel diffusion
This type of test may still give a positive precipitin result on a blood stain that is 10-15 yrs or older blood
Gel diffusion
Personal imprints and impressions found at crime scenes identify or tend to identify a person or vehicle….
As having been at the crime scene
Markings left on a surface by protruding parts of a person or a vehicle?
Imprints
Below are examples of what?
Bloody handprints, footprints,
Tire tread marks left behind after the tire has been contaminated with oil or mud
Imprints
What are the Steps of evidence retrieval of imprints
First photograph
Lifted by dusting with contrasting powder
Apply clean, sticky, transparent tape to dusted area to pick up
Press tape to a clean card to preserve it
*the object with the imprint sometimes can be transported to the laboratory
These are made by a person or an object in a material softer than the item of evidence making the impression.
Impressions
These are examples of what?
Tire tracks or foot prints in snow or soft dirt
Impressions
What clues do A trail of shoe prints or footprints offer?
Size or weight of the person making them
Speed of movement
Any gait abnormalities
This super cooling phenomenon leads to a unique spheroidal formation that is generally not observed in the natural environment.
Exothermic reaction
Fingerprints found at a crime scene can either be ?
Imprints or impressions
Bloody fingerprints left on weapons or at the scene of a crime are called?
Contaminated prints
These finger prints are observable with the naked eye
Contaminated prints and plastic prints
Fingerprints that are impressions that a burglar might leave behind when his or her fingers come into contact with soft glazier’s putty around the edges of a window
Plastic prints
These finger prints are collected by first photographing then casting with dental plaster
Plastic prints
These types of prints usually cannot be seen by the naked eye and need to be developed to be seen
Latent prints
These fingerprints are caused by the transfer of body perspiration or oils present in finger ridges that are deposited on the surface of an object
Latent prints
Two types of surfaces to find latent prints?
Porous and nonporous surfaces
Ex of a smooth nonporous surface
Glass
Ex of porous surface
Paper
Latent prints on a smooth nonporous surface such as glass can be developed by
Dusting with a powder of contrasting color of the surface
Latent fingerprints found on porous surfaces such as paper are developed
In the laboratory through iodine fuming or ninhydrin process
When iodine fumes react with the ammo acids in the print, they appear
Purple when developed
Testing done on latent fingerprints of a porous surface that are done in the lab, where iodine fumes react with the amino acids in the print and appear purple in color when developed
Iodine fuming and ninhydrin process
T/f
Slippery surfaces such as plastic bags are resistant to the dusting process
True
Give an example of where a print may be found that is resistant to the Dusting process
Slippery surface of a plastic bag
A common glue product when heated in a covered tank resulting in fumes on a fingerprint and makes a print observable and photographable
Cyanoacrylate
The process in which a common glue is heated in a covered tank resulting in fumes that settle on a fingerprint making the print observable and photographable
Cyanoacrylate fuming process
Which type of print could be used with the cyanoacrylate fuming process?
Latent prints that are left on smooth slippery surfaces such as a plastic bag
What does Afis stand for?
Automated fingerprint identification system
This machine reads prints by placing a persons hands on a platen and a scanner that reads the print digitally
Afis
Afis has reduced the FBI’s ten- print processing time from?
45 days to less than 2 hrs
What are the traditional means of ingress of forced entry?
Windows, doors, and skylights
The Initial procedure for collecting marks of tools used to gain access
Locate accurately the impression and record the general description and measurements.
What is the key to identifying marks of tools?
Accuracy
In Tool mark, what could make an effective trial exhibit?
Cast impression of mark
What is the overriding factor in reporting and collecting tool impressions at the scene of a crime?
Preservation of the impression, or it’s reproduction for future comparison with a suspect tool
Prevailing practice of tools
Treat tools as suspects and collect it for laboratory comparisons
T/f
Second contact of a TOOL to an impression ruins the evidence
True
A form of trace evidence that is transferred between individuals and objects during the commission of a crime
Hair
Hairs are typically transferred during what type of crime?
Personal crimes such as sexual assaults physical assaults and homicides
DNA analysis can be performed on hair if
The root bulb is still attached
In the absence of DNA analysis, the crime laboratory would conduct
A microscopic analysis
What does A microscopic analysis of hair determine?
Origin Racial origin Age and sex Forcible removal Hair comparison
Which type of hair shows little variation and uniform distribution of pigment compared to other body hairs?
Head hair
The Origin of hair determines
What part of the body did the hair come from
This type of hair is usually straight or wavy, with fine to course pigmentation which is evenly distributed
Racial origin is Caucasian
This type of hair is normally curly with an uneven distribution of pigments
Racial origin- African American
A cross-sectional analysis of Caucasian hair demonstrates that it is
Oval to round shape
Cross sectional analysis of an African American hair demonstrates that it is?
Racial origin- Flat to oval in shape
The age and sex of a person’s hair cannot be determined with any degree of certainty with the exception of?
Infant hair
Why is infant hair an exception of identification of age and sex?
It is very fine and shirt and has fine pigmentation
When hair has been dyed or bleach, it may give identification of?
The sex of an individual, but not certainty of it
Examining what part of the hair could I’d whether it was forcibly removed?
Examining the hair root and shaft
What is more likely to be the result of hair normally falling out than forcible removal?
Absence of adhering tissue to the bulbous shape root
What is the most common request in hair determination?
Whether the hair found on the scene belongs to sp
T/f
It is not yet possible to individualize human hair to any single person through its structural characteristics
True
Hair growth estimate based on time since the hair was treated can be based on what rate?
One centimeter per month
T/f
Fungal and nit infections can further link a hair specimen to a particular person
True
Why is the examination of human hair most valuable?
It’s ability to exclude someone as a suspect in the commission of a crime.
Fibers are key items of evidence in personal crimes such as
Homicides, physical assaults, sexual assaults
In a case where a victim was bound with Rope, twine, or cloth backed tape, fiber analysis is important in determining?
The source of these materials
Name the two types of fibers
Natural and manufactured fibers
List the common natural fibers found
Wool and cotton
Which natural fiber is plant based?
Cotton
Name the common synthetic manufactured fibers
Nylon, acrylic, polyester
What is the first step in the analysis of fibers?
Microscopic examination with a comparison microscope
This is essentially two microscopes connected together side by side that allows two samples to be viewed simultaneously by the operator
Comparison microscope
What is used for a reliable method for analysts to compare the colors of fibers through spectral patterns?
Visible light micro spectrophotometer
Before the forensic scientist can reach a conclusion that two or more fibers compare, it must be shown that the fibers in question have…
The same chemical composition which can be determined by the use of infrared microspectrophotmetry technology
Name the two types of glass fractures
Radial and concentric
This glass fracture starts at the center or point of impact
Radial fracture
To glass fracture runs outward in a star shaped pattern
Radial fracture
This glass fracture forms concentric circular cracks around the point of impact
Concentric fracture
The location where the cone shaped crater is narrowest of a bullet that perforated a glass panel, indicates
The direction from where the bullet was fired
If a number of bullets hit a pane of glass, the sequence can be determined by
Examining the radial fractures
The radial fractures of the first bullet….
Stop by themselves or run to the edge of the glass
Subsequent radial fractures produced by other bullets will…
Stop at an already present radial fracture produced by the first bullet
Describe a fracture match
When glass splinters or shards found on suspect fill the void of glass at scene
What are some common characteristics examined to differentiate glass?
Density, refractive index, thickness, color, and chemical composition
Paint evidence is usually found in what form?
Smears or chips
T/f Usually only class characteristics can be determine by paint analysis
True
Which type of paint evidence is more useful?
Chips
Physical characteristics of paint
Color, layering , weathering, texture
Chemical properties such as solubility and composition can indicate
The type of paint and identify the pigmentation and fillers used in the manufacturing process
Paint Reference samples of automobiles help provide
Type of car with that paint
_— of a bullet hole in a glass window indicates the direction of travel
Cratering
T/f
A bullet enters from the small side of a crater and exits from the large side
True
In cases involving checks, the check itself is a ?
Questioned document
T/f
Documents that have been destroyed or partially destroyed by fire can never be restored by lab technicians
False, can sometimes be restored
Charred paper must be sprayed with
A preservative and requires special packaging and transport to the place of examination
What are the two types of proof used at criminal trial?
Direct and Circumstantial evidence
This type of proof involves eyewitnesses who have, through one or more of their five senses, experienced something relative to the crime
Direct Evidence
This type of proof is defined as evidence from which an inference can be drawn and which includes items such as physical evidence
Circumstantial Evidence
What are the major types of circumstantial evidence?
weapons, blood, imprints, or impressions, tool marks, hairs, fibers, glass, paint, questioned documents.
Name the two categories of Physical evidence
Class evidence and individual evidence
this type of physical evidence cannot be linked to a particular person or an object but only to a class of object
Class evidence
Glass, paint, shoe prints, ballistics, fibers, and tool marks are all examples of what?
Class evidence
firearms should be handled to preserve
ballistic identity
the identification of firearms, bullets, cartridges, and shotgun shells
ballistics
refers to the functioning of firearms through the firing cycle
interior ballistics
the study of projectiles in flight
exterior ballistics
what do ballistics use as the primary source of identification?
the inside of the barrel, the firing pin, the breech face in which the firing pin hole is located, the chamber, and the ejector and extractor.
firearms should be picked up by their
rough or checkered wooden portions or any external metal portion except the trigger guard and trigger area
emblems and symbols are _______ that indicate tests performed to prove the strength of the chamber of a firearm by actual firing with maximum loads
proof marks
refers to the diameter of the barrel of the gun and is also an identifying characteristic
caliber of the weapon ( or its gauge if a shotgun)
this test starts with applying adhesive tapes to the person’s hands. These tapes are then sent to the crime laboratory where they are examined using a scanning electron microscope interfaced with an energy dispersive x-ray
gsr. gunshot residue examination
this examination is used to search for the presence of the major components in a center fire cartridge
gsr. gunshot residue examination
what are the major components in a center fire cartridge?
antimony sulfide, barium nitrate, and lead styphnate as well as metallic particles of zinc copper or nickel.
this super cooling phenomenon leads to a unique spheroidal formation that is generally not observed in the natural environment.
exothermic reaction
