Locard’s Exchange Principle “When a person comes into contact with an object or another person, a cross- transfer of physical evidence can occur.”

Types of Evidence 1. Direct/testimonial: firsthand observations (eyewitness account, video camera, confessions) 2. Circumstantial: indirect evidence; implies a fact, but not directly prove it Physical – bullets, weapons, impressions Biological – body fluids, plant parts, hair Trace evidence

Trace Evidence Small but measurable amounts of physical or biological material found at a crime scene

Examples of trace evidence Human hair Animal hair Fibers Soil or plant material (pollen) fingerprints Body fluids (semen, blood, saliva, mucus) Paint chips Broken glass Chemical residue

Categories of Evidence Class Evidence Narrows identity to a group of persons or things Example: blood type Individual Evidence Narrow identity to a single person or thing Example: fingerprint

Crime Scene Investigation

The Crime Scene Investigation Team Who is at the crime scene? Police and possibly a district attorney. Crime scene investigators. Medical examiners. Detectives. Specialists.

The Seven S’s of Crime Scene Investigation 1. Secure the scene. 2. Separate the witnesses. 3. Scan the scene. 4. See that photos are taken. 5. Sketch the scene. 6. Search for evidence. 7. Secure the collected evidence.

Secure the crime scene

Separate the witnesses Do not allow witnesses to talk to each other Witness accounts will be compared Avoid witnesses working together to create a story Asked: who, what, where?

Scan the scene Determine primary and secondary crime scenes – Primary: where murder took place – Secondary: where corpse was found Where should photos be taken? Wear protective gear to prevent contamination of crime scene

Mark Evidence with Tents

See that photos are taken: Crime Scene Photography Show the scene exactly as it was when you first saw it If something was moved before you arrived, don’t try to reconstruct the scene – just take the pictures the way you see it Be careful not to destroy any evidence while taking photos

Outside the Scene Exterior of building Arial photos Pictures of all doors, windows and exits

Overall Shots – Outside the Scene Outside

Inside the Scene Begin with a view of the entrance Then photograph the scene as it appears when you first step into the room Next, move around the room to get photographs of all the walls (also show positions of any possible pieces of evidence) Photos of other rooms connect with crime scene

Overall Shots – Inside the Scene

Items of Evidence Take 2 shots: 1.Midrange shot: show how the item is related to its surroundings 2.Close-up: bring out details of item Take 2 close-up shots if marking or measuring device is used One shot without device, one shot with device

Evidence: Knife (possible weapon) Midrange Photo Close-Up (with ruler)

Sketch crime scene Make accurate rough sketch Note direction (N) and scale of distance Include relevant objects (body, doors, windows, furniture, immovable landmarks) Make final copy (on computer) for court N

Search for evidence Grid, strip or lane, spiral search pattern Use flashlight to find hair and fibers Use forceps, vacuum cleaner to collect evidence GridStrip or LaneSpiral

Secure the collected evidence Properly package, seal, and label ALL evidence! Liquid: airtight, unbreakable containers Wet items (biological): dry out in breathable container Dry item: bindle  plastic or paper container Seal with tape and labeled with pertinent info

Packaging Evidence 1. Crease a clean paper and place the evidence in the X position (as shown above). 2. Fold in the left and right sides, and then fold in the top and bottom. 3. Put the bindle into a plastic or paper evidence bag affixing a seal over the opening. 4. Write your name on the seal. Bindle: folded paper used to hold trace evidence

In order to present credible evidence in court, a chain of custody log is essential. 1. A person bags the evidence, marks it for identification, seals it, and signs it across the sealed edge. 2. It is signed over to a technician in a lab for analysis who opens it, but not on the sealed edge. 3. After analysis, the technician puts it back in the evidence bag, seals it in another bag, and signs the evidence log (above, right). Chain of Custody

Crime Scene Evidence Direct or circumstantial evidence? Physical or biological evidence? Class or individual evidence?