This article was reviewed and updated for accuracy and readability in September 2017.

Have you ever seen CSI: Crime Scene Investigation? If not, find an episode online. It’s an exciting, intriguing show where investigators solve crimes almost entirely through forensic evidence. But does Hollywood have it right? What exactly does crime scene investigation involve?

The ultimate goal of a crime scene investigation is to convict the perpetrator (the person who committed the crime) by reconstructing the crime. Evidence, such as hairs and fingerprints, needs to be preserved and later analyzed in a lab. That might sound tedious, but remember, no two crime scenes are ever the same.

At the crime scene

The investigation begins once a special police officer called a Crime Scene Investigator (CSI) arrives on the scene. First, they make sure the scene is secure - that is, not tampered with. They conduct an initial walk-through and visually analyze the situation.

Next, they do a second walk-through and take photographs and sketches. Then, they collect all potential evidence carefully and package it for the lab. Finally, at the crime lab, all the evidence is analyzed. Once the results are in, the CSI leads the detective on the case.

Did you know? A CSI never works alone. They interact with detectives, medical examiners, police officers, technicians, and specialists on a daily basis.

What about all that invisible blood?

Although there may be a lot of unbelievable technology used in CSI on TV, a special chemical called luminol is completely real. Luminol reveals invisible blood traces because of a light-producing chemical reaction between several chemicals and hemoglobin (oxygen-carrying molecule) in the blood.The theory behind it is that the reactants (the original molecules) have more energy than the products (the resulting molecules). The reactants get rid of the extra energy in the form of light photons.This process is called chemiluminescence.

Did you know? Chemiluminescence is the same phenomenon that makes fireflies and light sticks glow.

Investigators spray suspicious areas and then turn off all the lights and block the windows. Blood traces will actually emit a bluish-green glow. This will not help investigators solve the case, but it can help them learn what type of weapon was used. For example, the blood splatter from a knife is much different than that of a gun.

However, this process is not without its problems. On the show, the CSI seems to spray many suspicious surfaces. But in real life, the luminol can actually destroy evidence in the crime scene. It is often used only after other options have been exercised.

Other differences between TV and reality

The use of luminol is one example of how real-life CSI is different from the TV show. There are other examples, too.  For example, in real life, you can’t determine the time of death within hours(even though on the show, this happens in almost every episode).

Also, on the show, the CSI appears at the scene of the crime and just starts searching. But in real life, they start searching only after a search warrant has been approved - and that can be a long process!

Lastly, on the show, the CSIs frequently interview witnesses. In real life, CSIs deal directly with evidence only. They would not be responsible for interviewing witnesses.

Although possibly not the most believable shows ever to have been on television, the CSI shows were fascinating. So too is real-life CSI! Crime scene investigation is truly a complex and fascinating field. And who knows? With today’s drastically improving technology, maybe some of the things you’ve seen on television today will one day be more real than you think!

This article is based on an article originally published on January 23, 2012. It was researched and written by Christina D'Ambrosio. Christina is a graduate from the University of Western Ontario with her degree in Biology. She is currently working for a pharmaceutical company.

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Luminol: a chemical that glows in the dark when it reacts with the right substance (ie: blood at a crime scene)

Hemoglobin: a protein in our red blood cells that help carry oxygen throughout our bodies.

Chemiluminescence: the scientific term for chemicals that glow in the dark (or emit a light) when a reaction occurs.


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