Douglas P. Lyle

Ever wonder just how prevalent various crimes are? Or about what you should do if you witness a crime? This Cheat Sheet covers that and more, such as how investigators approach a crime scene and the tools they bring to bear in their search for clues, as well as how the medical examiner or coroner determines the cause, mechanism, and manner of death.

The first step in gathering evidence is finding it, and that means taking an orderly approach to searching the crime scene. Many items, such as corpses and weapons, may be readily visible, but others, particularly smaller materials or bits of trace evidence, require diligence on the part of investigators. In homicides, investigators target points of entry and exit and the area near the body; in robberies, open safes, cabinets, or drawers are good starting points.

After doing an initial walk-through of the crime scene, the investigator begins mentally formulating a hypothesis of the crime, focusing on the likely sequence of events and the locations and positions of everyone present during the crime. Information like the following may be critical in determining the truthfulness of a suspect or the reliability of a witness: Shoeprints may reveal a perpetrator's every step.

Evidence is anything that can be used to determine whether a crime has been committed. Evidence may link a suspect to a scene, corroborate or refute an alibi or statement, identify a perpetrator or victim, exonerate the innocent, induce a confession, or direct further investigation. All evidence is not created equal.

While a crime scene is being processed, everything that transpires is documented in notes, sketches, and photographs, and perhaps even videoed. This documentation includes not only the scene and the evidence, but also the surrounding area, particularly the perpetrator's possible entry and exit points. A designated note taker keeps an accurate account of all activities in and around the crime scene.

Every person who handles evidence must be accounted for and recorded as a link in an unbroken chain of custody, from crime scene to courtroom. Without a continuous record showing that evidence has been kept safe and secure from the crime scene to the lab and ultimately the courtroom, evidence may be rendered inadmissible in court.

No body means no crime, right? Maybe so, but more often it means a body was well hidden. When a body (and the critical evidence it provides) can't be found, investigators rely on a few time-tested techniques for unearthing it. This branch of forensics is a particularly interesting one, and it's growing all the time.

If you need to find out how a victim died or identify a piece of a plant found at a crime scene, you call on a forensic scientist trained in pathology or botany, respectively. Professionals who work in the various forensic biological sciences are among the most highly trained and skilled members of the forensics team.