Forensics for Writers: the Crime Scene
Forensics for Writers: Part II
I left you last week standing at the edge of the crime scene. You are poised to step into it, but before your character can take that first step, there are things you the author need to know, even if the character doesn’t.
First, you have to decide the role your character is playing at the crime scene. Is she an investigator? A private eye? The victim (presumably not of a murder, but I’ve read stranger books)? The perpetrator? If your character is the lead investigator, they will be bounded by the laws of the land, and the procedures of their department. Failing to comply will lead to the loss of the evidence in court. The fastest way to throw your evidence out is to have it become the ‘fruit of the poisoned tree’ or less poetically, procured through illegal search and seizure.
On the other hand, your unscrupulous detective type might very well just stroll in, uncaring. Your victim is the crime scene, and the perp at least thinks he’s in control in making it. The forensic science is likely to prove him wrong in that. Once the author has the role straight, let’s begin.
Investigators are taught that you start taking notes – one of the three main ways to record a crime scene – even before you enter the scene. You begin with the statement of the responding officer(s) and possibly witnesses. Once you walk into the scene you are recording what you see, feel, and hear. Smells, an ephemeral impression, have to be captured immediately before they fade. Cigarette smoke in a non-smoker’s house. Gasoline at an arson scene… As they walk through the first time, the investigator is not touching anything. He is taking notes, possibly photographing, and beginning a rough sketch. Those are the three ways he will record (video is rare, and usually done later) the scene.
After the first walk-through, the fine details are filled in through the use of detailed photography and searches. Inside a residence, there is usually one or two investigators on scene. More will interfere with evidence and will be excluded. This isn’t always an easy job if there are higher-ups that want to come see a scene for some reason (high-profile cases, for instance) but a log of who entered the scene, when, and why, must be kept as part of the chain of custody.
Out of doors, searches become a bit more complicated and can involve many more people depending on what you are looking for, and over how much ground. The most common types of searches are grid searches, line searches, and quadrant searches, but which one is used depends on the terrain, what your investigator is looking for, and the manpower available.
What are you looking for? Physical evidence. Once something – a hair, a toolmark, a blood spatter – has been determined to be evidence, there are several things to do before the evidence is collected. The investigator needs to make notes about it, map it on his rough sketch, which includes specific measurements so the scene can be recreated later, and photography. Photographs should be taken of the evidence first without a scale (ruler or some object to show the size of the evidence) and then with a scale.
As you can imagine, this is a tedious and time-consuming process. Fictional accounts of forensic science tend to gloss over the crime scene, and as a writer, it is for good reason. Unless something your investigator does or sees here is vital to the plot, or you want to describe a bit of it to set the scene (heh) for the reader, you really don’t want to write a blow-by-blow account of recording evidence and collecting it.
And collecting it is the final step, as in essence your investigator is destroying the scene in order to analyze it in more depth than he can do at the crime scene. In touching the evidence, he runs the risk of altering it or destroying it, which is why it must be recorded first. But as in the other steps, collection of evidence has its own methods that must be adhered to, or risk destroying the evidence. Anything wet, whether its blood, water, mud, or other fluid, must be placed in paper bags. We are taught to never use plastic for biological evidence as it can break down DNA through heat and moisture, or mold and bacteria can grow on /in it. Once it is fully dried (there are drying lockers back at the evidence room for this very purpose) then it can be packaged in sealed plastic. At an arson scene, debris that may contain volatile accelerant must be put into sealed metal cans – paint cans work nicely for this (clean new ones of course!), and there are special lids made with a rubber gasket in the center that allows volatile gases to be drawn out with a syringe rather than opening and losing the evidence. Those are not used often – they are expensive and most departments are operating on a tight budget.
During collection, every item is handled and packaged separately. Every package must be properly labeled to maintain chain of custody, which is vital in making sure your evidence can remain admissible in court. The evidence tags and seals will be signed by every person that touches this evidence, and the marks also indicate where the evidence was located so the crime scene may be recreated faithfully. Evidence is not the only thing that must be collected at the scene. Reference samples are an important part of comparison when the evidence reaches the lab. Reference samples are from known sources and serve as standards, and some are substrate controls (most common in arson) which show that the surface of an area was not contaminated prior to the crime.
I’ll close out this week with Locard’s Exchange Principle. Dr Edmond Locard developed the idea in roughly 1940 that every time there is a contact, there is a transfer. People transfer hair, fibers, blood, fluids… both the suspect to the victim, and the victim to the suspect. At our fictional crime scene, as in a real one, there is a clue. It may be microscopic, and the investigator may miss it, but it is there.