I’m really interested in forensics and would love to write a short story on some kind of criminal investigator, but I realize I’ve never really gotten a grip on how the whole process works.
So, to ask morbidly: A witness finds a dead body with clear foul play, they call the police, what happens next?
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Have you watched even one episode of CSI or it’s countless offshoots?
I’m a first year student in a forensic science course at my university and it is honestly a really interesting question you’re asking. The short answer is: it’s dependent on way too many factors and variables.
Let’s say you’re a crime scene investigator called to a murder scene and there’s a dead person. So, what do you do? Collect evidence and minimise contamination. There’s so many kinds of evidence you can collect that it’s a little ridiculous. There’s the obvious ones, like lifting fingerprints from the murder weapon or recovering a sample of blood to test whether it belongs to the victim or another individual.
Then you have other techniques and routes you can take, all dependent on the circumstances of the crime. Maybe you’ve noticed some shoe prints near the point of entry of the house. You can (and should) collect this evidence by lifting the shoe print with a special tape or by using a casting agent and making a mould of the impression of the shoe print if its an indentation foot print (a 3D foot print, like in snow or mud). With this print, you can study the sole pattern of the shoe and search for little indications of wear and tear on the bottom of the shoe that make that shoe unique to absolutely any other in the world. Something as small as a little cut in the sole of your shoe at a specific spot because you stepped on some broken glass one time will make your shoe unique to any other shoe. The police can then compare this footwear mark to others on a footwear database, or to a suspect’s shoes (if there is a suspect in this case). Forensic scientists can even learn about your gait (how you walk, such as putting more weight on the inside or outside of your soles) just by looking at the marks of your shoes.
If there’s a tool mark somewhere in the scene, like when a hammer is hit against the wall, the crime scene investigator can similarly cast a mould of the indentation and study the mould under a microscope. Every tool that is manufactured will have small striations on it that will make them identifiable, so you can possibly determine what tool (or at least what brand of tool) made that mark. Furthermore, you can study the head of this hammer to look for paint chips that are resting on it after it hit that wall. Obviously, if a suspect claimed to own this hammer but claimed to not have hit that wall, the presence of paint chips from that wall on the hammer would support the idea that the suspect was involved.
Let’s say you find little fibres from clothes at the murder scene. You can lift those fibres with a tape and study them under a microscope, looking at their colour and structure. Then, you can take a control sample of fibres from the suspect’s clothing and compare the fibres from the suspect’s clothing to the fibres at the scene. If they match up, the chances are that the suspect was at the scene.
Similar to fibres, the suspect’s clothing can be analysed for tiny shards of glass. These little glass fragments can be compared to the broken glass of a hypothetical broken window in a house using different scientific techniques like GRIM (glass refractive index measurement) to confirm that the the glass from the house and the glass from the clothing are of the same composition, and thus likely the same window.
There’s an abundance of ways evidence can be collected, but some of it becomes less available than others after time. Trace evidence like fibres can be blown away in the wind because they’re so small, so it’s important that a crime scene investigator collects the most fragile evidence first and avoids contamination of the scene by wearing PPE (personal protective equipment) and following a bunch of boring yet important guidelines and precautions. Once evidence is collected, it’s given over to forensic laboratories and the intelligence gained from that can then be circled back to the police if need be.
One cool technique I learned about figuring out time of death is pollen deposits on the corpse. Very cool and sciency.
They’ll send a patrol officer first to verify there really is a dead body there and it’s not a false report. Probably fire rescue and an ambulance too on the off chance the person might still be alive. Probably a few more officers to tape off and secure the scene and make sure no on touches it until Crime Scene gets there.
The whole drawing a chalk line around the body thing is a movie trope and never really happens in real life
Am Norwegian cop, have done some crime scene forensics work when professionals were unavailable but that’s not my speciality. These days I mostly do digital forensics, that’s a quite different field. The following is more from a “first unit on the scene” perspective.
It depends, lots and lots of factors go into how the scene is handled.
First and foremost though, is checking to see if the person really is dead and providing first aid if there is any chance they might be saved. Often it’s obvious they’re dead, but with a fresh corpse you generally assume they’re alive until a doctor says otherwise. Up until you’re sure they’re dead, lifesaving efforts have priority over preserving evidence- but even so, you try to minimise disturbance of anything that could be important for the investigation if you can. And you take note of what gets done where, to the best of your ability depending on just how hectic the situation might be. Again, trying to save life has priority over finding out who did it.
Also, if the suspect is or could be nearby then making the scene secure has high priority. Don’t want the bad guy to unexpectedly emerge from another room while you’re working on the crime scene, and anyway you need to be sure there’s no other victims or perhaps a witness hiding somewhere. Or grief-struck family members who might need to be gently but firmly steered away from the scene. So sooner or later, there is usually a quick search of the premises and immediate surroundings while taking note of where you step and trying not to disturb anything. Gotta be sure there isn’t some terrified person hiding in the attic or whatever.
Set barrier tape around the perimeter, make a larger perimeter than you think you need. Often a murder weapon or other important item is left near the scene, you don’t want curious onlookers to mess with that so it’s better to start big .
Once you know there’s no further lives at risk, nobody to be saved and no other people at the scene, you freeze the scene and stay out of it until enough investigative resources have arrived and until there’s a plan for how to process the scene. Only then does the real forensics work begin, you can’t have people wandering in and out doing random stuff without a plan and without the skills to do it right.
While you wait for CSI, start writing down what you have seen and experienced particularly in regards to who has walked where and touched what along the way. These notes will be helpful to the forensics people later. Photograph your boot soles, and those of anyone else that have been at the scene including medical personnel etc if possible. Forensics will need those pictures, so they can rule out shoe prints left by first responders. Write down the names of bystanders and potential witnesses, if you have time then start taking some statements from anyone that have something to say. It might be a while to wait.
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