Books and Articles by 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 officer to arrive at a crime scene must take certain steps to preserve life and evidence. Only after these duties are performed can analysis of the scene begin. These steps include: Ensuring the officer’s personal safety and that of any fellow officers, victims, suspects, and witnesses. Offering first aid to any injured persons and calling for medical help.

Because forensics is such a hot topic these days, millions of viewers are becoming armchair experts on that subject. But is Hollywood reliable? Sometimes yes, sometimes no. The quick death A gun is shot or a knife is thrown and down goes one of the bad guys, perhaps clutching his chest or taking one last dramatic breath, but either way, he's instantly a goner.

Forensic analysis of most physical and biological evidence is conducted for two purposes: identification and comparison. Identification determines what exactly a particular item or substance is. Is that white powder cocaine? Is that brown stain dried blood? After testing, a forensic examiner may state that the substance in question is present, not present, or that testing was inclusive and the presence of the substance can't be ruled in or ruled out.

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.