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CSI: Facts

What is CSI?

Two Officers

Crime scene investigation is a science known as forensics. For every crime there is evidence left behind that can help authorities reconstruct the facts behind the incident. Skilled professionals analyze every bit of the scene until they know all the details of a crime including, sometimes, who did it. Let's take a look at this fascinating job and the science behind it.


Crime Scene

The word forensic comes from the Latin word forensis meaning public. It's related to the word forum, which in ancient Rome was a market, a place of public discussion, or a court. So our modern term forensic, which we use to mean the use of scientific methods in solving crimes, has its roots in the Latin words for making something public or bringing something to court. Today, any science that is used in the field of law is a form of forensic science.



Forensic scientists study lots of evidence at the scene. Their first line of fact-finding is to talk to anyone who was a witness or might have been a witness without realizing it. Witnesses can offer important clues. Sometimes the victim makes a good witness. But because people can forget or remember events incorrectly, physical evidence is usually more reliable.

Try this with a friend. Show your friend a photograph containing a number of people — say 3 or 4 — doing something in a location not familiar to your friend. Allow them to look at the picture for under a minute. Don't tell them why. Then ask them detailed questions about the picture. What color was the hair of the tallest person in the picture? What was the person wearing that was sitting? Which person had a hat? See if your friend caught all the details you are searching for. See why witnesses don't always get everything right. They didn't realize they were going to be a witness when the event was happening. Fear and other emotions can also affect a person's memory.


Some of the evidence that can exist at a crime scene:

  • Soil
  • Finger Prints
  • Glass
  • Plants
  • Fibers
  • Fingerprints
  • Tire tracks
  • Splatter
  • Footprints
  • Liquids
  • Chemicals
  • Handwriting
  • Drugs
  • Bullets
  • Hair
  • Blood
  • DNA
  • Broken or bent objects

These are just a few of the things that a forensic scientist might find and study at a crime scene.

Cross Contamination


When studying a crime scene, it is extremely important that evidence doesn't get cross contaminated. This means that evidence doesn't get mixed with other evidence, or that it doesn't get touched or moved by people who are on the scene. To prevent cross contamination, crime scene tape is placed on the site to keep people from walking into or touching any part of the area being investigated.

Investigators take other precautions too, like wearing gloves so their own fingerprints don't end up on the evidence. Each piece of evidence that they collect is stored in a separate plastic container before taking it into the crime lab to study further.

Other Challenges

Crime Scene

Outdoor crime scenes present some difficult challenges for investigators. Animals or other humans can accidently cross through a crime scene and destroy evidence before the investigators get word that a crime has been committed, especially in public outdoor areas like parks.

Time is crucial — having to investigate an outdoor crime scene at night when it is dark may cause forensic experts to overlook important evidence, but waiting until morning light allows weather conditions like rain or temperature changes to alter evidence.

When is it used?


TV programs would have most people thinking that crime scene investigators are hunting for clues in a murder or a kidnapping. That is often done, but forensic scientists can also solve cases involving burglary, break-in, car jacking, poaching, bank robbery, fraud, forgery, a traffic accident, and many other crimes.

Forensic scientists have even been called on to identify dinosaur bones, crimes committed centuries ago or to determine the cause of death for historical celebrities such as ancient kings and pharaohs.



DNA is often used to identify victims or suspects or to rule out people involved in criminal activities. But what is DNA and how can it be used in such instances?

DNA is like a secret code that exists in all of our cells. DNA is a microscopic instruction plan that holds details about us such as what we look like, what hand we write with, and even how tall we will grow to be. Everyone and every living thing have DNA. No two people have the same DNA unless they are identical twins. Because every living thing's DNA is different, it is used by investigators to determine the identifying details of a person, from hair color to gender. Scientists are currently working on discovering all of the secrets that DNA holds. Learn more about how DNA is used in forensic work.

In forensics, scientists can take a sampling from the inside of someone's cheek or their blood and compare the DNA of one sample to the DNA of another sample to be able to tell if they came from the same person. This can be very helpful in proving that a suspect is actually NOT guilty. This method of crime solving has been used regularly since 1992.



Fingerprints are the small ridges on the tips of our fingers and are different on every person. When a person touches a table or another surface, they leave behind a telltale sign of their fingerprint. Forensic investigators can remove this fingerprint using a special powder and some tape. They then compare this evidence with a fingerprint that has already been collected from the person to whom they are planning to compare.

Fingerprint specialists evaluate the small curves and whorls of the fingerprints to determine if they are the same. There are a series of fingerprint patterns which are similar in all people. Take a look at these patterns to learn more about fingerprinting.

Wildlife Forensics

Fox and Hen

Crime in the animal world happens more than most of us know. Forensic investigators use the same methods and tools as those who solve crimes against people. They can find out how an animal died, how long ago it happened, and track down if it was killed by another animal or by a human. By teeth marks and hair left at the scene, they can even figure out what kind of animal did the killing. Sometimes it is important to find out if a wolf or a bear is killing farm animals or is in an area frequently visited by hikers or campers. This is a safety issue for all of us who love the outdoors.


Animals are sometimes hunted illegally. This is known as poaching. A forensic scientist can use evidence left at the scene of a dead animal to help authorities arrest the person or the people who killed an endangered animal, hunted more than they were permitted, or who was hunting outside of the rules.

To learn more about wildlife forensics visit Idaho Fish and Game's forensic website.

Want To Be a Forensic Scientist?

Here are just a few of the possible jobs available in the world of forensic science:

  • Medical examiner — performs autopsies
  • Chemist — analyzes chemicals found
  • Forensic engineer — can determine how a structure collapsed
  • Toxicologist — tests for poisons
  • DNA analyst — uses DNA to identify victims or suspects
  • Lab technician — studies blood and other body samples
  • Computer technician — records digital information for safe keeping
  • Fingerprint expert — identifies specific patterns in fingerprints
  • Handwriting expert — determines handwriting patterns
  • Psychiatrist — studies crimes and the people involved to help prevent future crimes
  • Anthropologist — studies bones to determine age, gender, race, etc.
  • Ballistics expert — determines the gun and ammunition used in a crime

Magnifying Glass

Lots of other professionals can be called on in particular situations — plumbers, electricians, nurses, doctors, dentists, and anyone else who might have information specific to the details of a case.

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