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Crime Scene Investigation

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Presentation on theme: "Crime Scene Investigation"— Presentation transcript:

1 Crime Scene Investigation
Chapter 2

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


4 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


6 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


8 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


10 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.


12 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


14 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


16 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


18 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

19 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


21 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

22 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


24 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


26 Reconstruction Once evidence is collected and 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


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