Three Ways To Solve A Crime: Part 1 — Physical Evidence

This is part one in a three-part series overviewing how investigators solve crimes. If you haven’t read my post covering the role of evidence in criminal investigations, I recommend you start there first!

Imagine walking into an unoccupied house for the first time and being tasked with finding out what happened in that same house three days earlier. No one is there for you to speak with, and the closest neighbor is several miles away. When there are no people to interview, the investigator must turn to the physical environment for clues about what might have happened and what to do next.

As we know from our discussion about evidence, it can be pretty much anything. Physical evidence is no different. From fingerprints left at a crime scene, text messages stored on a cell phone, corporate records filed with state commerce officials, trace amounts of DNA found on a discarded soda can, or the search history left on a web browser, physical evidence comes in all shapes and sizes.

NOTE: Many times you might hear a distinction made between ‘physical’ evidence and ‘electronic/digital’ evidence. For the purpose of this discussion, I am including electronic/digital evidence under the parent category of physical evidence, as it will always require a physical medium to be captured, analyzed, and reported on.

Physical evidence serves three primary purposes: (1) it helps to identify individuals who could have relevant information about the crime under investigation, (2) it provides independent corroboration of witness testimony, and (3) in some cases, it can provide real-time documentation of a crime and solve a case nearly all by itself.

Identification

One of the most practical uses of physical evidence is for the identification of individuals who were either involved in a crime or those who might have further information about a crime. Back to our earlier scenario about walking into an unoccupied house and being tasked with figuring out what happened three days ago, the easiest way to answer that question is to find someone who was at the house three days ago and ask them what happened. So then, our first step would be to search for physical evidence to help us identify such people.

We might start by looking for pieces of mail sent to the house and get some names from there. We could quickly pull property tax and vehicle registration records for the address to gather additional names as well. Every house needs electricity and water service, so gathering the names of individuals currently paying the utility bills for the residence would also be a logical place to look. Within the house itself, we could start searching for documents containing people’s names, phone numbers, and other identifying information and make note of those too. All this would be a way of leveraging physical evidence to identify individuals who might have more information about what happened.

Corroboration

Once we gathered our list of people to interview and talked with them, some might tell us a story about what happened at the house three days ago. But how do we know if we should believe them? After all, if we’re investigating a crime, isn’t it logical to think that some people might not tell us the truth? Do we have to take everyone at their word?

Of course not! That’s where we turn again to physical evidence to either confirm or deny witness testimony. This is called corroboration in investigative parlance. It answers the question of whether the physical evidence aligns with what the witness told us they saw happen.

Let’s say we identified Jane as the owner of the house. We talked with Jane, and she tells us that three days ago she left her best friend Susan alone at the house from 2PM to 4PM. We then interview Susan who denies being at the house anytime in the past month. Given the two conflicting accounts, we might turn to both women’s cell phone geolocation records to help figure out which one is telling us the truth.

Knowing that most people keep their cell phones with them regularly, we might pull records from the service providers to confirm the location of each phone three days ago from 2PM to 4PM. If Jane’s phone was located away from the house and Susan’s phone was located at the house, that would give us a pretty good indication — corroboration — that Jane is being honest and Susan might have something to hide. In this case, it would also be worthwhile to follow up with further analysis of Susan’s phone records to identify other individuals Susan was in contact with between 2PM — 4PM and who could have more information to help us out.

Documentation

What I’ve just described is a fairly common and iterative process utilized during criminal investigations. Use physical evidence to identify witnesses — interview witnesses to identify additional witnesses and physical evidence — use physical evidence to corroborate or disprove witness testimony — rinse — repeat.

At the end of this process, we’re generally left with a few witnesses we judge as trustworthy because the evidence backs up their testimony. But wouldn’t it be better if we didn’t need to rely on people telling us what they saw happen at the house three days ago? What if we could see what happened ourselves? Welcome to the upper echelon of the physical evidence world — real-time documentation.

What I’m talking about here is evidence that tells us what happened all by itself — video recordings of the incident in question, text messages between two suspects talking about the incident as it happened, photographs — all those kinds of things. We live in an age where many aspects of our public (and even private) lives are recorded, saved, and shared. As such, it is becoming increasingly common to find criminal acts recorded (in part and in their entirety) as they occur. In many ways, it’s hard to do much of anything nowadays without it being documented to some degree. And when investigators can locate those golden nuggets of physical evidence, it’s case closed.

Remember my earlier suggestion to scour Susan’s phone records and identify anyone else she might have been in contact with between 2PM — 4PM? Turns out she was texting back and forth with another friend named Lisa and sent her some pretty incriminating videos that she made during those two hours. Even though Susan had already deleted the recordings from her cell phone, Lisa had not. And those were the videos you needed to solve the case.

So, when you find yourself working with physical evidence, remember it’s all about understanding what you’re trying to accomplish — keeping the end goal in mind. After you have a grasp on that, just start following the breadcrumbs. Evaluate each piece you come across with respect to how it applies to the identification of involved parties, corroboration of witness testimony, and documentation of the incident itself. With a little patience and hard work, you might surprise yourself with what you find.