Criminalistics Exam 1

Forensic evidence

• can be anything

Expert witness

• an individual whom the court determines to possess knowledge relevant to the trial that is not expected of the average layperson

General acceptance

• the Frye standard has the court decide whether the questioned procedure, technique, or principle is appropriate and meets the guidelines for the relevant scientific community

Biology unit of the crime lab

• staffed with biologists and biochemists who identify and perform DNA profiling on dried blood stains and other bodily fluids, compare hairs and fibers, and identify and compare botanical materials such as wood and plants

Processing a crime scene

1. securing and isolating the crime scene

2. recording the crime scene

3. conducting a systematic search for evidence

Scientific method

• a process that uses strict guidelines to ensure careful and systematic collection, organization, and analysis of information

People prohibited access to crime scenes

• anyone who is not authorized investigative personnel

Duties of the first responding officer at a crime scene

• responsible for preserving and protecting the area as much as possible

• first priority is to obtain medical assistance for individuals in need and arrest the perpetrator(s)

Rough sketch drawings

• a draft representation of all essential information and measurements at a crime scene

• this sketch is drawn at the crime scene

Videotaping crime scenes

should include…

• the entire scene and the immediate surrounding areas

• long shots and close-ups (should be taken in a slow and systematic manner)

• 8 second pano

• remove audio

Proper collection and preservation of evidence

• each piece of clothing should be handled carefully and wrapped separately

• critical areas of the crime scene should be vacuumed and the sweepings submitted to the laboratory for analysis

• fingernail scrapings from individuals who were in contact with other individuals may contain minute fragments of evidence

4th amendment

• “the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizure, shall not be violated, and no warrants shall issue, but upon probable cause, and the persons or things to be seized”

IBIS

• integrated ballistic identification system

• the heart of NIBIN (national integrated ballistics identification network)

• allows firearms analysts to acquire, digitize, and compare markings made by a firearm on bullets and cartridge casings recovered from crime scenes

Comparison

• the second step in the examination of physical evidence

Class characteristics of evidence

• properties of evidence that can be associated with a group and never with a single source

Comparison analysis and common origins

• this kind of analysis subjects a suspect specimen and a standard/reference specimen to the same tests and examination for the ultimate purpose of determining whether they have a common origin

CODIS

• combined DNA index system

• enables federal, state, and local crime laboratories to electronically exchange and compare DNA profiles, thereby linking crimes to each other and to convicted offenders

Blood spatter direction of travel

• determined by the pointed end of the bloodstain

Impact spatter

• occurs when an object impacts the source of the blood

• the most common type of bloodstain pattern found at a crime scene

Common types of blood stains

• passive (droplets, pools, trails)

• transfer

• impact

Area of origin

• the area in a 3-dimensional space from which the blood was projected

Back spatter

• also called blow-back spatter

• blood directed back toward the source of the force that caused the spatter

Cast-off patterns

• created when a blood-covered object flings blood in an arc onto a nearby surface

Void patterns

• created when an object blocks the deposition of blood spatter onto a surface or object

Contact blood patterns

• created when a surface that carries wet blood comes touches another object that does not have blood on it

Identification techniques of a deceased

• can determine sex by the size and shape of various skeletal features (i.e. pelvis, skull/cranium)

Stippling or tattooing

• the result of soot and gunpowder that leaves markings around the bullet hole

Defense wounds

• occurs when the victim attempts to fight off the attacker or block assaults

• typically on the victim’s outer forearms

Carbon monoxide

• extremely toxic gas

Temperature loss after death

• 1-1.5 degrees per hour

Lividity

• coloring of the body

• sets in around 16 hours after death

Rigor mortis

• stiffening of muscles

Causes of death at fire scenes

• asphyxia caused primarily by the extremely toxic gas, carbon monoxide poisoning

Ridge characteristics

known as minutiae

Ex:

• ridge endings

• bifurcations

• enclosures

• other ridge details

Fetal fingerprint development

• develops and enlarges during weeks 14-24

Latent prints

• a fingerprint made by a deposit of oils and/or perspiration

• invisible to the naked eye

Plastic prints

• ridge impressions left on a soft material (i.e. putty, wax, soap, or dust)

Loops

characterized by ridge lines that enter from one side of the pattern and curve around to exit from the same side of the pattern

must have 1 delta

• 2 types:

  • ulnar loop

  • radial loop

Whorls

• characterized by ridge patterns that are generally rounded or circular in shape

• must have at least 2 deltas

• 4 types:

  • plain whorl

  • central pocket loop whorl

  • double loop whorl

  • accidental whorl

Arches

• characterized by ridge lines that enter the print from one side and flow out the other side

• 2 types:

  • plain arch

  • tented arch

Developing latent fingerprints

• fingerprint powders

• iodine fuming

• ninhydrin

• physical developer

• superglue fuming

Physical biometrics

• fingerprint

• hand

• iris and retina

• facial scans

Behavioral biometrics

• handwriting

• voice analysis

• gait recognition

Iris and retina scans

• iris biometrics is replacing retina biometrics because it is all-around better technology

• problem with retina scans: viable images can be affected by disease

FBI FACE program

• facial analysis, comparison, and evaluation services

• provides face recognition capabilities, among other things, to support active FBI investigations

List the 3 basic functions of a forensic scientist

• Analysis of physical evidence

• Providing expert testimony

• Furnishing training in the proper recognition, collection, and preservation of physical evidence

Explain the difference between identification and comparison

• Identification is used for the determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit

• Comparison does the same kind of testing on specimens, but it is for finding whether they have a common origin.

What determines the size of blood drops in a cast-off pattern

• The size of the drops are directly related to the size of the point from which they were propelled.

  • Drops propelled from a smaller or pointed surface will be smaller and the pattern more linear

  • Drops propelled from a large or blunt surface will be larger and the pattern wider

Briefly describe the processes of algor mortis, livor mortis, and rigor mortis

• Algor mortis – the body temperature continually cools until it reaches the ambient or room temperature

• Livor mortis – the settling of blood in areas of the body closest to the ground

• Rigor mortis – stiffening of muscles

Why is it pointless to try to obscure or obliterate one’s fingerprints by scarring or otherwise damaging the skin?

• It would be impossible to obliterate all the ridge characteristics and permanent scars provide new characteristics for identification