Crime Scene Investigations Chapter 2

Chapter 2.1 Crime Scene Evidence

Locard’s Exchange Principle Every contact leaves a trace! Whenever two objects come together they must affect each other in some way. Something is likely to be exchanged between them!

Principle of Individuality Two objects may be indistinguishable, but no two objects are ever identical. Things can be put into classes or even individualized in useful ways.

Frye vs. Daubert Daubert - “Does it work?”; Frye - “Do scientists like and use it?” FRE If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based sufficiently upon facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case.

What is Evidence?

Crime Scene Evidence

Role of Forensic Evidence  1.  2.  3.

What’s Wrong with the Previous Slide?

Forensic Science SHOULD BE used  To test whether, rather than to establish that, a particular person or thing was at a particular place at a given time.  To test whether, rather than to establish that, something was done with a particular tool: e.g., this bullet could have come from this weapon, this cutter could have sliced this tape, this letter may have been typed on this printer.  To test whether a relationship exists between people: e.g., that these people could be siblings, or that this person is likely to be the child of those parents.

Types of Evidence Physical evidence is generally recognized to be a material object such as a weapon, fingerprint, or item of clothing. Must be recognized at crime scene.

Identification Analysis Focuses on Identifying the relevant features of a piece of evidence with as much specificity and certainty as possible, leading to:

Comparison Analysis

Match key features found in an unknown sample with candidates from a very large pool of known possibilities Examples include fingerprints, DNA profiles, eye iris patterns, handgun firing pin patterns, automotive paint profiles, and biometric information.

Comparison Analysis Verification or authentication focuses upon comparing a set of features observed to a known sample with just one reference sample i.e. comparing the scratches on the sides of a bullet with one test fired from a suspect hand gun.

Comparison Analysis Important to determine chance that a purely random match of the features between two unrelated samples would occur.

Class Characteristics

Individual Characteristics Criminal with AB- blood type, left handed red- haired male reduces suspect pool to.0014% of population.

Analyzing Evidence

Fingerprint Identification

Analyzing Evidence

Chapter 2.2 Legal Evidence

Warrants Can only be issued with probable cause

Search Warrants

Special Circumstances that Allow Warrantless Searches

Mincy v. Arizona (1978) Drug bust that went wrong and an undercover police officer was killed. Police spent 4 days searching and seizing evidence (without a warrant) Mincey arrested and convicted. Supreme Court ruling:

Michgan v. Tyler (1978) Building destroyed by fire was put out in early AM. Building left unsecured until 8 AM when a preliminary search was done (for cause of fire). Subsequent searches (at 4, 7, and 25 days) removed additional evidence. Tyler convicted of arson. Supreme Court:

Chapter 2.3 The Evidence Collection and the Evidence Team

Processing the Crime Scene

Secure and Isolate the Scene Should consider the crime ongoing until it is determined otherwise Providing emergency medical treatment has priority over preserving evidence.

Secure and Isolate the Scene Once safe, role of first responders is to preserve the crime scene and evidence- establish a perimeter.

Secure and Isolate the Scene A lead investigator must be designated who then defines the crime scene boundary (better to make larger) Investigators need to document everything: weather conditions, locations of objects, witnesses, etc.

Record the Scene

Azimuthal Locating- uses a compass arrangement, such as used by surveyors, to locate the evidence by measuring angles and distances to a known geographic point.

Record the Scene Can also use coordinate mapping and electronic methods. Need to construct a detailed map pf the scene, starting with a rough sketch and field measurements. Helps to give juries a detailed picture of a crime scene.

Photography

Search for Evidence The goal is to not miss or damage any potential evidence. Properly record and collect anything relevant to the case- difficulty is sifting through what is significant. Better to collect too much rather than too little.

Collection and Preservation of Evidence Different types of evidence require differing methods of packaging and storage based upon the characteristics of the evidence.

Collection and Preservation of Evidence

Chain of Custody (CoC) Forms a continuous and provable record of every moment in the evidence’s existence after its collected.

Evidence Teams Each person on the team has a well-defined set of tasks and responsibilities. A crime scene processing unit needs to be well organized and a logic based operation. Team leader, photographer, sketch/mapping preparer, evidence recovery and recorder personnel, and specialists

Specialists May include: – Anthropologist – Blood expert – Bomb technicin – Criminalist – Engineer – Entomologist – Medical examiner – Odontologist – Surveyor – Etc.

Types of Crime Scenes