Students and Educators: The Basics of Crime Scene Investigation - U.S. Fish and Wildlife Service Forensics Laboratory

THE BASICS OF CSI

To understand what happens at a typical crime scene investigation, it’s important to understand a few basic elements:

The purpose of CSI
The basic CSI tasks
The basic premise of CSI
The inherent problem of CSI

The Purpose of CSI …

Determine if a crime has occurred
ID the victim(s)
ID the suspect(s)
Collect evidence related to the crime
Re-enact the events of the crime
Link suspect, victim & crime scene

The Basic CSI Tasks …

Protecting & searching the scene
Evaluating the scene & evidence
Documenting the scene & evidence
Preserving & collecting evidence

Protecting & searching the scene, documenting & scene and evidence, and preserving & collecting the evidence are all considered the mechanical aspects of CSI.

Evaluating the scene & evidence is considered the thinking aspect of CSI.

Ideally, a crime scene investigator should be thinking (evaluating) at all times while conducting the mechanical aspects of CSI; but it is all too easy for a crime scene investigator to fall into the trap of working mechanically … especially at a large/complex crime scene containing dozens or even hundreds of evidence items.

The Basic Premise of CSI …
It is impossible for suspect, victim and crime scene to come together — usually in a violent manner — without the transfer of physical (trace) evidence.

It is this premise that ensures investigators that a careful investigation of a crime scene is worth the effort. The evidence will be there; it just has to be found and carefully/properly preserved and collected.

The Inherent Problem of CSI …
Every investigator (or EMT, reporter, neighbor, etc.) who enters the scene has the potential to damage evidence and leave or pick up trace evidence.

In effect, a CSI cannot expect to enter a crime scene without adding to or subtracting from the available evidence. The trick is to be thoughtful, careful and persistent.

Okay, now that you understand the basics of CSI, let’s take a closer look at the characteristics of those evidence items being collected.