470 likes | 1.21k Views
Crime Scene Investigation. Crime Scene Investigation : Main goal is to gather evidence that can be used to identify and convict the person(s) responsible for a crime. What is Crime Scene Investigation?. Who’s at the Scene of a Crime?. Police Officers – first to arrive, secure the scene
E N D
Crime Scene Investigation: Main goal is to gather evidence that can be used to identify and convict the person(s) responsible for a crime. What is Crime Scene Investigation?
Who’s at the Scene of a Crime? • Police Officers – first to arrive, secure the scene • CSI Unit – documents & collects evidence • District Attorney – determines if search warrants are necessary, secures warrants from a judge • Medical Examiner – may be present to determine a preliminary cause of death • Specialists – may be called in if evidence requires special analysis • Detectives – interview witnesses and investigate the crime
Preserving and Isolating the crime scene Responsibilities of 1st Officer arriving:1. obtain medical assistance for anyone in need2. arrest any perpetrators3. exclude all unauthorized personnel4. isolate the area “yellow tape”– do not cross
So, what exactly needs to be done at the scene of a crime? • Crime scene investigator will conduct an initial walk through • (conditional/transient evidence is noted ex: lighting, smells, sounds, temperature of body are noted) • Investigators will interview witnesses, first responders or victim • During the second walk through, the scene is thoroughly documented through drawings, notes, photographs, and digital video.
Observing and documenting the scene • Investigators will examine the scene for evidence, identify points of entry and exit. • Good technique is to use oblique lighting. (beam of flashlight is swept back/forth@ an angle 1 inch of the surface in a semidark area)
Notetaking Most important parts of processing a crime scene. It includes: • detailed written descriptions of crime scene w/ locations of physical evidence including : • time of discovery • who found it • who packaged and marked it • disposition of item after being collected • must be detailed (step by step of investigation) enough to refresh one’s memory months years after processing • tape or video recording is advantageous but at some point it must be transcribed
Photographs and Videotape • Photos can capture details that even the most observant investigators may miss. • Photographs should be taken before touching or moving any evidence. • All photos should include a ruler for scale
Sketches • Once photos have been taken, the crime-scene investigator sketches the scene • * Sketch has essential info & measurements at a crime scene. -- sketch is drawn at the crime scene. -- shows dimensions & location of objects. all sketches should include date and time, scale, reference points, distance measurements, the names of investigators, victims, suspects and legends.
Searching for Evidence Typical examples of crime scene search patterns are: 1. Line search: used in large open areas 2. Grid: double line search 3. Zone method: effective in houses or buildings. Teams are assigned rooms or small zones to search
Search for evidence 4. Wheel or ray: best in small areas. Officers begin at the center and move outward in a pattern that makes a circle 5. Spiral method: best used in areas where there are no barriers or wall. Officers move inward or outward
Crime Scene Search Patterns SPIRAL GRID LINEAR
So, what exactly needs to be done at the scene of a crime? There are several different methods of search patterns used during the examination of the scene.
Collecting and packaging evidence • Each different item must be placed in separate containers to prevent contamination. • plastic pill bottles, vials, manila envelopes and plastic bags are excellent for collecting evidence. The most fragile items (fingerprints, bloodstains, and other trace evidence must be collected first)
Collecting Evidence 1. Evidence can be massive to microscopic 2. may only be detected in a crime lab ex. traces of blood on clothing, hair and fibers from vacuum sweeps 3. it is sometimes necessary to confiscate clothing from victim and perp • Critical areas should be vacuumed; sweepings from different areas must be kept separate 5. finger nail scrapings must also be taken from suspects and victims
Collecting Evidence 6. Trace evidence should be left on object unless it is attached to a large object; remove w/ forceps 7. Bloodstains • scraped if dry • transferred to moistened swab • cut out the area of object 8. Each item must be kept separately
Packaging Evidence Special consideration: • Wet evidence should NEVER be packaged in plastic containers while wet. • Bloodstained materials should NOT be stored in airtight containers b/c accumulation of moisture may encourage the growth of mold; in these instances wrapping paper, manila envelopes or brown paper bags are used. • All items of clothing must be air dried & place in individual separate bags. • Charred debris recovered from a fire must be sealed in airtight containers to prevent evaporation of volatile petroleum residue. (new paint cans or tightly sealed jars)
Collecting Evidence All evidence needs to be properly packaged, sealed and labeled. The evidence log should contain all pertinent information including: • Case # • Item inventory # • Description of the evidence • Name of suspect • Name of victim • Date & time of recovery • Signature of person recovering the evidence • Signature of any witnesses present
Chain of Custody An evidence log and a chain of custody document must be attached to every evidence container. *Chain of Custody the documented and unbroken transfer of evidence; list of all people who came into possession of an item of evidence (continuity of possession)
Chain of Custody • Seal the evidence & the collector’s signature is written across the sealed edge. • When the package is reopened at the lab it is opened at a location other than the sealed edge. Every time opened: new seal, new signature, place in new evidence bag.
So, what happens after the evidence is collected? • Once the crime lab has processed the evidence, the results are forwarded to the lead detective on the case. • It is up to the lead detective and his team to reconstruct the crime scene based upon the evidence and lab findings and determine who committed the crime. • Once a case is made, the person who committed the crime can be arrested and tried in a court of law.
How has careful review of a crime scene helped to convict a criminal? • A double murder – no fingerprints, no DNA, no murder weapon. The only thing that could link the killers to the crime were the fibers from the blankets.
Quick Review of evidence *Physical Evidence- any object(s) that can prove that a crime has been committed or can link a crime & its victim or its perpetrator.
Physical evidence includes • fingerprints • footprints • shoe prints • tire impressions • tool marks • fibers • weapons • bullets • and shell casings.
Biological evidence includes • body fluids • hair • plant parts • natural fibers.
Class Evidence Examples • Single layered paint • Soil • Hairs • Fibers
Individualize Evidence • Fingerprints • Handwriting • Bullets (striations) • Toolmarks (striations) • Shoeprints (wear patterns) • Tire prints • Glass fragments that can be matched
*Trace evidence small but measurable amounts of physical or biological material found at a crime scene.
What evidence would you collect? Mock Crime Scene: http://www.masss.gov