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.

Locating evidence can be straightforward: Someone calls the police to report a burglary, and when the police arrive the victim invites them in and shows them the location of the pried-open window, the family safe, and the perpetrator's escape route. But, in other cases, the probable location of the evidence is not always associated with a crime scene, and police are not invited into the area where the evidence may be located.

Staging is when someone who's committed a crime attempts to make the scene look like something that it isn't. The most common staging scenario occurs when someone tries to make a murder look like a suicide or an accident. The suspect may move the body or clean certain areas. Say, for example, a husband strikes his wife in the head with a blunt object, killing her.

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.

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.

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.

For those interested in digging deeper into the science and techniques of forensic science and criminal investigation, here are some excellent resources for further study. The Writers' Forensics Blog This is DP Lyle, MD's blog. Though originally geared toward writers of crime fiction, this blog is followed by forensics industry professionals and those who have an interest in crime and forensic science.

Many criminals attempt to damage, alter, or remove their fingerprints to avoid identification or connection to prints found at a crime scene. From John Dillinger to more "common" criminals, these efforts are usually unsuccessful. Still, if, after leaving prints at a scene, the perpetrator successfully alters or damages his prints, the fingerprint examiner may not be able to make a reliable match.