CSI Facts for Crime Writers

csi crime lab lavaOne of the most important things a a writer is to get the facts straight. It doesn’t matter if you’re a journalist or a novelist or a screenwriter–if you don’t research the facts, there will undoubtedly be at least one person in the audience who catches it, like the five scientists who exposed the less-than-scientific plot points of Prometheus.

That’s why I like to attend the crime lab workshops hosted by the Los Angeles Visionaries Association (LAVA). The workshops, which happen once every couple of months, feature presentations by top criminologists from Los Angeles. For someone who writes mystery novels, the information is worth more than the price of admission, certainly.

The most recent crime lab workshop, titled “The Killer Behind the Camera,” featured presentations on two murder investigations involving photographers who were repeat offenders. The facts of each case were grisly and sometimes hard to take, but I picked  up some scientific information that’s normally only privy to CSI professionals.

1. The blood never washes off. Lady Macbeth was right, that spot never does come out. At least not while there’s luminol around. If the name sounds familiar, you probably watch shows like Dexter and CSI. Luminol is a chemical that illuminates the copper and iron present in human blood, and is so sensitive that it can detect blood that is diluted to one part per million. When the chemical is applied to a surface, the strength of the glow depends on the concentration of blood remaining, but repeated applications can uncover even the most trace amounts. Really, no matter how often something is cleaned, it probably won’t be enough.

2. Luminol is not the go-to blood test for field work. Although incredibly effective, the chemical is carcinogenic, and therefore not used as frequently as TV shows would have you believe. (Really Bones writers? A whip-smart pregnant scientist toting around a carcinogenic chemical?) The more commonly-used test is the Castlemeyer test, which is an oxidation reaction that occurs when hemoglobin binds with the chemical phenylphaline and hydrogen peroxide. Trace amounts of blood turn bright pink. (Fun fact: the Castlemeyer test can register a false positive for potato.)

3. Crime scene photography is methodical and all-inclusive. When photographing evidence on a crime scene, photographers must capture literally every angle of a subject: it must be photographed from overlapping angles covering all four compass points and all vertical angles, including oblique, 30, 60 and 90 degrees. By capturing a subject in this manner, it is possible to reconstruct a true 360 degree model, taking into account factors of light and shadow. In addition, a photographic scale with markers and a unique number must be placed in all photographs to verify that they are original and were taken at the scene.

csi crime lab lava4. DNA takes a while to process. You can’t get the results back in a few hours. The minimum time for a DNA result is 5-6 days because the lab has to copy the DNA, and then the lab’s findings need to be reviewed by other scientists to make sure that they followed the proper technical and administrative procedures. In real life, results typically take months, but rush cases can be pushed through in about 10 days.

5. The DNA in semen is in the sperm. At first glance, this doesn’t seem to be an interesting detail, but I have one word for you, crime writers: vasectomy. You can have that plot twist, just thank me in the liner notes.

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