Second test Flashcards
How can a trace evidence be classified as ?
A class ( General ) evidence or an individual (Precise) evidence
Why analyze a trace evidence?
For physical and chemical properties.
What can be used to identify physical evidence ?
A microscope and a Microspectrophotometry ( Paint chip analysis )
What are the different types of microscopes ?
Binocular microsope, basic one. Comparison microscope, polarized light criscope ( brings out details), Scanning electron microscope ( determine mineral elements) , steremicroscope ( 3d appearance to the object)
What are the different parts of a microscope ?
Base, ocular, pointer, body tube, nosepiece, objectives, arm (2), stage, stage clip, coarse adjustement, fine adjustement, iluminator (go see the notes for the graph)
What are the different step to using a microscope?
- Make sure that the low power objective is clicked into position under the body tube.
- Place the slide (cover slip up) into the clips on the stage and center the slide over the light opening.
- Using the coarse adjustment knob, raise the stage as far as it will go.
- Looking through the ocular, use your coarse adjustment to lower the stage until the specimen comes
clearly into view.
5.
Obtain a sharp focus using the fine adjustment.
6.
Regulate the light intensity by raising or lowering the illuminator or changing the dial on the base.
Reducing the light will usually give greater contrast. - These microscopes are parfocal so once the specimen is clearly in view under low power, no major
adjustments are necessary. So, to increase magnification, be sure the area you want to examine is
centered and then turn the nosepiece until the next higher power objective locks in position. The
material should now be in view and should require only slight focusing with the fine adjustment.
NEVER FOCUS WITH COARSE ADJUSTMENT WHEN USING MEDIUM OR HIGH POWER. - Before removing the slide, always return the microscope to low power and turn the coarse
adjustment knob to lower the stage to allow sufficient access to remove the slide
What are the three parts that compose a hair ?
The roots, the shaft and the tip ( in this order)
What are the three layers of hair ?
The cuticule ( the outlayer, gives hair strenght). Cortex ( largest portiong=, 2 layer. Gives color with melanin), Medulla ( central core)
What are the different types of cutitcule ?
Coronal ( crownlike), found amongs rodents. Spinous ( petalike) found in cats, Imbricate ( flattened like stones) humans
In the cortex, how the melanin level impact the hair color ?
Brown and black : high level
Blond and red : low level
White and grey : zero
What are the different types of medulla ?
Fragmented, intermittent, continous and absent. ( go look to see them )
What is the medulla human usually have ?
An absent one.
What are the techniques used for chemical testing ?
X-rays, infrared spectrophotometry, neutron activation analysis.
How to match hair samples ?
- Obtain hair sample from the suspect ( about 50)
- Compare with the hair found : the color, widht, lenght, diameter, distribution pattern of the medulla and its shape, color and distribution pattern of pigment in the cortext, cuticle pattern.
What are the two class for fibers ?
- natural ( Plants, animal source)
- Manmade (manufactured, synthetic)
What is important to know when collecting fibers ?
After 4 hours, 80% of the fibers are gone. After 24hours, 95%. It is important to act fast.
What do we use to collect fibers ?
Using tape, vaccuming and tweezers.
What do we compare fibers ?
Their shapes, diameter, color, shininess, curs and crimps.
What are the other types of trace evidence ?
Glass, paint chips, soil and plants
What can glass tell us ?
Point of entry or exit, what broke it, fingerprint, shoeprint, DNA
What can paint tell us?
What is the car, if the car is painted in a special paint can be a individual evidence.
What are 3 types of pattern evidence ?
Class, individual, wear.
What are three types of fingerprint evidence ?
Latent, ( not visible), Visible, plastic
How to preserve pattern evidence ?
- Take a picture
- Lift the impression using adhesive lifter or gelatin lifter.
- If not possible, use a electrostatic lifting device for chair, walls and floors.
- Chemical development
- Casting
What are the steps to cast something ?
1- An aerosol is sprayed on the print to harden it
2- The dental stone is prepared by mixing water with the powder
3- The mixture is mixed by hand to reach the appropriate consistency
4- Using a spoon to disperse the flow, the mixture is poured in
5- The cast is allowed to dry (24 -48 hrs) before removal
How blood moves under physics ?
It follows the law of physics. It travels like projectiles. It lands differently depending on the size, velocity, angle etc.
How blood behaves chemically ?
Blood clots once out of the body. It seperates with the hard red clot and the yellow serum. If blood liquid : a few minutes have passed. If blood jelly like, up to an hour have passed. If seperated into clot and serum, more than an hour.
What is inside the blood ? molecular components
Proteins used to identify and DNA. Can also tell if drugs.
What is a passive bloodstain ?
A bloodstain that follows gravity. It moves with ONLY gravity. Depending on the angle of impact, the stain will be very different. 15 degrees =very long with a little tail telling which direction it comes from. 90 degrees = small circle. The material changes also : glass will be smooth but concrete will be messy. The higher, the bigger bloodstain.
What are the three types of projected bloodstains ?
Low velocity (removing knife from body ) , medium velocity (internal bleeding), high velocity (getting shot).
What are the three types of spatter ?
Impact spatter ( from the impact) Projection spatter ( caused by blood being thrown by a weapon ) combination spatter ( both )
What is a transfer bloodstain ?
when a object soaked in blood moves and come in contact with another object.
How to find the location of the victim when the crime occured ?
Using the point of convergence and the point of origin.
A blood spatter has its own unique what?
Directionality and impact angle
Directionality
the course the blood drop followed
Impact angle
slant at which the blood drops strike the surface
Point of convergence ?
A 2D representation tracking the directionality if two or more spatters.
Point of origin?
A 3-D representation of the point where lines tracking both the directionlaity and the impact angle of two or more spatters.
How to determine the point of origin?
1- Find the area of convergence for the stain pattern
Draw straight lines through the long axis of several individual blood stains, following the
line of their tails. The area of origin will be on a line straight out from this area
2- Place a pole or stand as an axis coming from the area of convergence
3- Attach one end of a string next to each droplet
4- Lift the string until it lines up with the determined angle of impact (protractor) and
attach the other end of the string to the axis pole
S- Strings appear to meet: point of origin
Error of 2 feet
What is a void pattern ?
An empty space in the middle of a blood spatter where blood should be
What can a void pattern indicate?
- The location where the assailant blocked the spatter
- Where an object was but moved
- Location of the victim being attacked
- If a body was moved
What is blood made of ?
55 % of plasma ( White blood cell, red blood cells)
45 % yellow liquid remaining after blood clotted
What are the different blood gorups ?
- A, B, AB, O
A?
Anti serum B, can give to A, AB, can receive from O, A
When does agglutination happen?
When antigen comes in contact with a anti ( Antigen A and anti serum A )
Rh - or + which can give to the other
Rh- can give Rh+, the contratry no.
If a Rh - gets Rh+, what will happen ?
The first time, nothing. The second time, bacon.
If a mom ab and a dad A, what is the possibility?
AA, AO, AB or BO genotype
A, AB or b phenotype
Why is blood useful in forensic ?
Helps determine if the blood is human or animal, if chemical were used.
What are the two type of blood test to find blood on the floor etc?
Presumptive tests : colour and fluorescent tests
Confimatory tests : teichmann and Takayama
What are the different tests to find semen ?
-presumptive tests : Testing for acid, testing for spermine and choline
Confimatory tests : Microscopic examination
Prostate-specific antigen
What can also help about semen ?
Timing ( sperm live 4-6 hours in a living victims) 2 weeks in a corpse Secretor status ( 80-85%) have their ABO type in the fluids.
Saliva ?
Only presumptive test, can have DNA, ABO type if secretor
Vaginal fluid ?
Only presumptive test
What are the different categories of guns ?
Handgun ( one hand), rifle ( use a lever ), shotgun ( doesn’t fire bullet, fires sheels filled with bellets
What are the info that can be obtained from a bullet?
Type of gun used, trace evidence ( paint, fibers), DNA from small bits of flesh and blood
What are the 4 types of bullets ?
Lead bullet ( Soft, deform when strike target) Lead alloy bullet ( Lead + other metal, deform less than lead bullet) Semijackted bullet (expand on impact) Fully jackted bullet ( covered in brass, penetrate very well, can penetrate some body armor)
What are the info that can be obtained by a shell casing?
The impression left by the firing in
Breechblock patterns
Headstamps
Extractor marks
What is a rifling pattern?
Land and gooves, twists, striations created by the bullet leaving the gun that can link the gun and the bullet
How to compare striations :
1) Obtain an intact bullet fired from the suspect weapon
2) Compare the lab-fired bullet next to the crime-scene bullet using a comparison microscope
3) A match (3 consecutive striations) means that you have identified the weapon
4) This may lead to the identification of the perpetrator
GSR testing :
Lost after only 2 hours, can be wiped
Gunshot wound are dangerous?
Usually, death occurs rom exsanguination or infection, the bullet itself is rarely fatal.
What are the 4 types of gun wound?
Muzzle two feet away : a halo around the hole
6 inches to 2 feet : speclekd due to gun powder
6 Inches or less : hole plus charring around the hoke
pressed : charring and ripping around the hole.
