Trace Evidence By Taylor Martin and Samantha - PowerPoint Presentation

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Trace Evidence By Taylor Martin and Samantha - PPT Presentation

H umphreys What Is Trace Evidence Trace evidence is the materials or markings that are left behind when different objects or materials come into contact with one another This usually occurs due to friction ID: 646738

crime evidence forensic trace evidence crime trace forensic analysis web apr 2012 http fibers scene pollen people residue paint

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Slide1

Trace Evidence

By Taylor Martin and Samantha

umphreysSlide2

What Is Trace Evidence?

Trace evidence is the materials or markings that are left behind when different objects or materials come into contact with one another.

This usually occurs due to friction.

Photo collage representing fibers, paint chips, gunshot residue and ignitable liquidsSlide3

Locard’s Exchange

Dr. Edmond

Locard

(a.k.a. the Sherlock Holmes of France) was a pioneer in forensic science and created the principal “every contact leaves a trace”.

Dr. Edmond

Locard

(1877-1966)Slide4

How It Is Used

Used to determine:

people,

places,

objects,and substances involved in a crime.Slide5

Main Categories

Fingerprints

Hair

Plant fibers

GlassPaintSoilPollenFootprintsTire marksGunshot

Explosive residue

Blood splatterSlide6

Fingerprints

Fingerprints are unique for every person (even for identical twins)

Left at the scene by perspiration, body oil, etc.

Traditional ink fingerprints usually collected by the police.

Types of fingerprintsSlide7

Visible Vs. Latent

visible

Can be seen by the naked eye

Latent

Has to be captured by powder, laser beams, etc.Slide8

Hair

DNA taken from strand to match other samples

Shows if the person has dyed their hair

Can also be used to determine race/ethnicity

Scanning electron microscope image of human hairSlide9

Plant Fibers

Clothing fibers are used to link people to crime scenes

Types of fabrics distinguished by microscopic examination

Types of fibers under a microscope: mercerized cotton (blue strand in the top right corner), rayon (red strand in the centre), linen (forming a V) and wool (left).Slide10

Glass

Pieces of shattered glass can be reconstructed

Hole left in window can determine what shattered it (e.g. bullet, someone falling through, etc.)

Broken window with a bullet holeSlide11

Paint

In a hit and run, paint can be used to find the make and model of a car

Paint is often transferred to tools during a break and enter

Paint scrape on a carSlide12

Soil

Soil sticks to shoes and is used to tie people to crime scenes and other places of interest

Soil samples of various climates and geographical regionsSlide13

Pollen

Pollen is dispersed by plants all the time and can connect people to where they’ve been

Can be used to tell if drugs are from the same supplier

Drawings of some pollen shapes as seen under a microscopeSlide14

Footprints

Used to determine the shoe size, brand and model

Reveals a way a person walks; can be used to tell if they are injured or healthy

A forensic officer holds a cast of a shoe print at a crime scene.Slide15

Tire Marks

Easily find the make and model of the tires from the tread

Show any distinguishing characteristics: gouge, nail, rock, smooth patch, etc.

Find speed of the vehicle before incident/impact

Three types: acceleration marks, breaking marks, yaw marks

Skid marks on a roadSlide16

Gunshot Residue

GSR on a person’s hand shows that they fired a gun

The hand is swapped for particles then later analyzed by microscopeSlide17

Explosive Residue

Crime scene is examined (usually swabbed) to find traces of materials used to make a bombSlide18

Blood Spatter

Will show the direction of falling blood by angle of impact

What part of the body it came from

Type of weapon used

Number of blowsSlide19

Blood Splatter

Can pin people to the scene of the crime with residue

Reveal if object at the scene were moved in any way after the incident

Show were the victim and the perpetrator were during the action

Can also tell the tale of the eventSlide20

Preservation

Photographs are used to be analyzed in the lab later

Once objects are photographed they are put into evidence bags for collection

Assorted sizes of paper evidence bags for collection of “wet” evidence (items in contact with body fluids)Slide21

Accidental Contamination

Many steps must be taken to avoid contamination of evidence

Methods of preventing evidence contamination by police and investigators include wearing suits over clothing, slippers over shoes, and wearing latex gloves.Slide22

Analysis Of Evidence

Macrophotography

Microscopic analysisSlide23

Bibliography

Acadiana

Crime Laboratory, Louisiana, Arizona Department of Public Safety, Bureau of Alcohol, Tobacco, and Firearms, et al. "Forensic Fiber Examination Guidelines."

SWGMAT: Scientific Working Group for Materials Analysis

. Web. 10 Apr. 2012. <http://www.swgmat.org/Forensic%20Fiber%20Examination%20Guidelines.pdf>.

"Bloodstain Pattern Analysis (BPA)."

Royal Canadian Mounted Police

. Web. 06 Apr. 2012. <http://www.rcmp-grc.gc.ca/fsis-

ssji

fis-sij

/bpa-ats-eng.htm>.

Bryant, Vaughn, and Gretchen Jones. "Pollen - Nature's Tiny Clues."

ASU - Ask A Biologist

. ASU - Ask A Biologist, 21 Dec. 2009. Web. 10 Apr. 2012. <http://askabiologist.asu.edu/pollen-and-solving-crime>.

Blair,