Crime Scene Investigation Chapter 2 THE CRIME SCENE

Crime Scene Investigation Chapter 2

THE CRIME SCENE • CSI’s carefully and systematically sift through a crime scene in order to learn: – How and when the crime was committed – Who committed it and why – What items may have been removed from a crime scene • The methods used by anthropologists, archaeologists, and historians are similar to those used at a crime scene

THE CRIME SCENE (2) • There must be a plan for systematically searching the site • Safety of the searchers must be considered • Only highly qualified and trained people should conduct the search • Contamination must be minimized • Time may be of the essence • The scene must be thoroughly documented • There must be a chain of custody for each piece of evidence

A Crime Occurs & Is Discovered • Crimes can be discovered in one of three ways – A witness sees it and reports it to the police – A victim of the crime reports it to the police – The police discover the crime in progress • Police may also “discover” a crime with a sting operation – A scenario whereby criminals are encouraged to commit crimes that they probably would have done anyway

The First Officer at the Crime Scene • Determine if the perpetrator is still there – Hot search (immediate) or cold search (interview witnesses) • Tend to the injured • Secure the scene to prevent contamination • Do not walk through the scene and search for evidence • Note any obvious safety hazards and warn others

Crime Scene Investigation • After a crime scene has been discovered and protected, CSI’s will arrive • If there is a dead body, a forensic pathologist will – Certify the death – Determine the postmortem interval (PMI) – Take photographs and collect trace evidence • The CSI unit takes charge of the scene • Each member has a defined role: – Sketcher, photographer, searcher, documenter, fingerprinter, blood spatter analysis, etc.

Preliminary Scene Examination • The first duty of the CSI at a crime scene is to conduct a preliminary examination – Safety hazards must be addressed and remediated – Boundaries of the crime scene must be ascertained • Perpetrators often carry evidence away and there may one or more secondary crime scenes

Systematic Search of the Scene • Must be carried out in a way that minimizes alteration of the scene • Photograph as early as possible • Determine the search pattern that will be used – If it is a room, a spiral or back-and-fourth pattern may be used – Outdoor scenes are often divided into grids • Avoid covering the same ground more than once to minimize contamination

Recording the Crime Scene • Two basic methods – Freehand sketch including measurements of various objects – later translated into a scale drawing – Still photography including many pictures at different distances and angles under various lighting conditions • Hand drawn sketches are still used, but computers are often used to create scale drawings • Crime scenes are often videotaped

Collection of Evidence • Evidence is of little or no value if it is contaminated or degraded • At some crime scenes (especially homicides) forensic scientists work with CSI’s to process evidence • There are three major steps in the process of evidence collection –Recognition –Collection –Packaging/preservation

Recognition of Evidence • How do investigators know what is evidence and what is not? • Homicides, burglaries, sexual assaults and other crimes usually have some characteristic types of evidence – Weapons, blood, fibers, hair, fingerprints, tools, glass, soil, body fluids • There is no such thing as too much evidence • The exact location of the evidence must be recorded

Collection • As much evidence as possible should be collected • Lack of sample size may limit testing – The defendant is given a chance to have their own tests performed, so if it is used up, it is excluded from trial • Probative value (significance of evidence) is greatly enhanced if it can be linked to a known material or object

Packaging & Preserving Evidence • There are physical, scientific, and legal requirements that determine how evidence should be packaged • All evidence must be authenticated – Chain of custody – Uniquely identified to avoid confusion with other evidence • Tamper-evident packaging must be used

Preserving Evidence • Packaging must be designed to preserve the evidence • It may be weeks or months before the evidence is analyzed • Different types of evidence require unique packaging to preserve it – Living plants, wet blood or body fluids, wet paint, trace evidence, powder, fire residue

Reconstruction • Once evidence is collected analyzed, investigators will attempt to reconstruct the crime – Identities of the victims – Identities of the perpetrators – The sequence of events that took place • The focus is to link the suspect to the crime and build a case that will stand up in court beyond a reasonable doubt