If you're writing a murder mystery, you need to know how your investigator will go about solving the crime. I've already covered steps one through four. Today's post is on step five, the gathering of evidence. I'm taking this information from the Whodunit book called Murder one: A Writer's Guide to Homicide by Mauro V. Corvasce and Joseph R. Paglino.
A bunch of this you already know from watching CSI or other cop shows. Detectives are looking for any detail that might help them solve the crime, including footprints, clothing fibers, strands of hair, blood samples, paint chips, substances transferred from the perps clothing to the scene, etc. Sometimes the detective can analyze the evidence himself (like footprints or tire impressions). Other evidence needs to be analyzed in a forensics lab.
Whether you're using an officer, a detective, or a crime tech in your book, they need to wear gloves and paper booties over their shoes so they don't contaminate the scene by adding their own footprints and fingerprints. Any evidence gathered is placed in paper bags, plastic bags, Ziplock bags, plastic bottles, jars, anything that can be sealed and documented with the name of the person who collected it, where they collected it from, and the date it's collected. It's transported to the police station, where another officer signs for it and puts it into the evidence locker or sends it off to the crime lab. This is called the chain of evidence, and anyone who handles the evidence has to sign that he/she has done so. It's used to ensure the reliability of evidence if it's ever used in a trial.
On CSI, every piece of evidence they collect is useful in solving the crime. That's not the case in real-life situations, and you shouldn't make it the case in your book. In an enclosed crime scene, like a house or apartment, evidence will be collected that has nothing to do with the crime, but it has to be analyzed anyway. Dirt just inside the front door might be transfer from a perp, or could be what the dog tracked in earlier. Fingerprints on the window lock could be the perps, or could be the bedroom's resident who likes to sleep with the window open every night. Cigarette butts in an ash tray could belong to a stupid criminal, or could be Grandpa Joe's from his visit yesterday.
If the crime scene is outdoors, evidence gathering gets exponentially more difficult. Is that soda can just a piece of garbage from a passing litterbug, or did the perp toss it there? Was that spot of dog doodie transferred from the perps shoes, or the vics shoes, or from the shoes of a witness? Did that bit of bloody gauze come from the killer or from the paramedic who tried to save the victim's life?
The hard part for the writer is knowing how much useless stuff to toss into the book. Too little, and it's unbelievable. Too much, and you bore the reader. I brought up something two paragraphs before that should also be dealt with here. Most murderers think they are too smart to get caught. They've covered every base, gotten rid of every bit of evidence, lined up the perfect alibi... but in reality, criminals are fairly stupid people. And they make mistakes. It's usually these mistakes that lead to their arrest, so make use of that in your book. That cigarette in the ash tray? The killer saw a tray full of cigarettes, figured the police wouldn't check them all, so he lit up to relax after all that hard work of killing his cousin's wife, snuffed it out in the ashtray, and takes off thinking he's in the clear. You can have quite a bit of fun with this, so use your imagination to come up with some ways your killer could accidentally implicate himself after he's supposedly sanitized the scene.
My next post is removal of the body. You won't want to miss that.
-Sonja
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