Forensics For Dummies
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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.

FBI crime index

Crime is a common occurrence in the United States. The FBI maintains a database of all reported crimes throughout the country. It’s called the Uniform Crime Reporting (UCR) Program. During 2013, nearly 10 million criminal acts were reported. These crimes consisted of the categories and numbers shown in the following table.

Crimes Number of Criminal Acts
Violent Crime 1,163,146
Murder/Manslaughter 14,196
Rape 79,770
Aggravated assault 724,149
Robbery 345,031
Property Crime 8,632,512
Burglary 1,928,465
Larceny-theft 6,004,453
Auto theft 699,594

Source: Federal Bureau of Investigations

The approach to the crime scene

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:

  1. Ensuring the officer’s personal safety and that of any fellow officers, victims, suspects, and witnesses.

  2. Offering first aid to any injured persons and calling for medical help.

  3. Calling for backup and any ancillary personnel, such as detectives, crime-scene investigators, coroner’s office personnel, and firefighters, that are deemed necessary.

  4. Cordoning off the scene to protect the integrity of any evidence.

  5. Detaining and separating any suspects or witnesses whenever possible.

  6. Establishing a security log for any and all persons who enter or leave the crime scene.

What to do if you witness a crime

Do you know what to do if you witness a crime? In life, you just never know. You could be going to the store or a movie, maybe dropping the kids off at school, or perhaps sitting at your desk at work, and it happens — a crime occurs right before your eyes.

Here’s what you should do:

  • Protect yourself. Run, call for help, or hide. Do what is necessary to keep yourself out of harm’s way.

  • Help others. Offer first aid to anyone who’s injured.

  • Call for help. As soon as possible, dial 911 to report the crime and to summon medical and law enforcement help.

  • Don’t touch or move anything. Remember that anything you touch or move can damage or contaminate critical evidence.

  • Pay attention. Take a deep breath, relax, and look around. Notice people, what they look like, what they’re wearing, any distinguishing marks they have, and what they’re doing. Notice vehicle make, model, and license number, or any other distinguishing details, if possible.

  • Wait for the police. When the police arrive, direct them to the crime and to any injured parties. Tell them exactly what you witnessed and answer all questions truthfully. Be careful to relate only what you know and don’t attempt to help by filling in any gaps with what you believe should be true.

The tools of the trade for crime scene investigators

Crime scene investigators are called to all types of crime scenes and at all hours. Because they need certain tools and equipment to perform their duties, criminalists usually keep a well-stocked toolbox, which contains the items they most often need. The box may literally be a toolbox or tackle box, but can be anything that is easily carried to the scene. Here’s what’s in it:

  • Crime-scene tape to cordon off the area

  • A flashlight

  • Latex gloves and paper shoe covers

  • A magnifying glass and tweezers for collecting trace evidence

  • A pen, logbook, and sketchpad

  • Measuring tapes and rulers

  • Digital camera, as well as a camera with black and white and color film and several different lenses

  • An assortment of paper, plastic, and glass containers to store collected materials

  • Sealable evidence bags

  • Portable alternative light sources such as laser, ultraviolet, and infrared

  • Basic fingerprint kit with powders and lifting tape

  • Casting kit for three-dimensional shoe and tire impressions

  • Gunshot residue detection kit

  • Chemicals to locate occult bloodstains — such as Luminol

  • Serology kit for sampling blood and other biological fluids

The cause, mechanism, and manner of death

The most important function of the medical examiner in any death investigation is determining the cause, mechanism, and manner of death. Here are definitions of each of these terms:

  • Cause of death: The disease or trauma that directly caused the victim’s death. Examples include a heart attack, a gunshot wound to the head, or a drug overdose.

  • Mechanism of death: The specific physiological derangement that actually led to the cessation of life. For example, a heart attack victim could die from a deadly change in heart rhythm or from severe damage to the heart muscle, leading to shock. Here the cause of death is a heart attack, but the mechanism is a cardiac arrhythmia or cardiogenic shock, respectively.

  • Manner of death: How the cause of death came about. The five manners of death are natural, accidental, suicidal, homicidal, and undetermined. A gunshot wound (the cause of death), may have been accidental, suicidal, or homicidal, for example. Only deaths from disease are natural.

About This Article

This article is from the book:

About the book author:

D.P. Lyle, MD, is the award-winning author of many nonfiction books and works of fiction. He is the co-host of Crime and Science Radio, and has worked as a forensics consultant with the writers of popular television shows such as> Law & Order, CSI: Miami, Monk, Judging Amy, House, and Pretty Little Liars. Find him online at

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