Under Arrest - F is for Forensic Science

Welcome to the letter F of the 2019 A-Z Blogging Challenge!

F is for Forensic Science: what does it include?

Collecting, preserving and analyzing evidence during an investigation. We talked about (physical) evidence yesterday: fingerprints, gunshot residue, DNA, clothing fibrers, etc.

Because evidence is so very crucial, there are strict rules on how to obtain, handle and preserve evidence:

First of all evidence needs to be obtained legally. Sounds like a no-brainer, but in fact, police is bound to strict rules. They can't just barge into a home and seize some drugs, for example. I'll talk about this in my W post: W is for Warrant. 

Law enforcement agents need to document and photograph the evidence. In criminal shows you typically see them using tools like markers and scales. Evidence is then placed into a paper bag or envelope, sealed and labeled. The examiner puts his initials, date and time across the sealed area. 

If the evidence is a bodily fluid ("biological evidence") like blood, semen, saliva or skin you collect it with the cotton tip of a Q-Tip and allow it to dry completely, otherwise it's going to be useless. 

Clothing items including shoes may be very helpful as they often contain all kinds of evidence: traces of blood from the victim and ideally from the killer as well (think stabbing), traces of plants or soil that indicate a certain area the person spent time (beach, park, industrial plant, railroad tracks). Each item is stored separately; tears and stains must be documented. (Missing threads may be found at the crime scene). 

Injuries on a patient or dead body are documented from head to toe: bruises, lacerations, abrasions, cuts, you get the picture. Examining a body can tell you so much about when and how this person died. In my X post (X is for X-Ray) I'll talk a bit about autopsies and the like. Oh man, what made me chose this topic...

A chain of custody form must be completed and maintained. Every person who worked on this case must be documented in order to make sure this evidence will in fact be admissible in a court of law. 

Let's put our newly acquired knowledge into action by applying it to the CSI NY epidsode "the Fall" (Season 1, episode 17):

The team investigated the robbery of a wine shop during which the owner was shot. They spot a surveillance camera and hope to gain some valuable info. While viewing the video (which comes in great color quality as it can only be the case in fiction) they not only see the faces of the criminals but notice a soda can left by one of the perpetrators.

However the can wasn't at the crime scene when the crime lab crew arrived (or else it would have been photographed, collected and labelled as we have just learned!) 

One gang member used one of his mates' names, so the investigators knew that one was called Hector. This was also confirmed by the dying wine shop owner who could even recall that this guy Hector had a prominent scar on his cheek. 

The CSI team establishes a time line which shows that there were only two minutes between the neighbor store owner's 911 call and the first responding police officer's arrival. Since eye witnesses saw the perpetrators flee on foot, it was impossible that they came back to retrieve the soda can.

So where was it, and who took it?

They pay the officer who was the first on scene a visit and ask for this log book which he hands over reluctantly. He is known to be a conscientious cop with a brilliant memory. In his notepad they find an entry that is crossed out. They find out that the inks used to take notes and to cross out this entry are different, so either it was done later or by another person. 

The crossed-out section said "Hector - soda can".


One explanation that would explain why a cop tampers with evidence was that he was being paid by the gang to keep them out of trouble, but the CSI team had been working with this officer for a long time, and they never had reason to believe that he was corrupt.

They start canvassing the area of the crime scene, and sure enough find the soda can in the trash not far from the wine shop.

The DNA specialist finds two things on the soda can:
  • Ephithelials from the cop (thin skin cells you typically lose all the time, and they sticks to items you touch, that's why professional criminals as well as investigators wear gloves.)
  • Saliva DNA indicating the person who drank from the can is a male relative of the cop's.
Whaaaaat? Bizarre, right? 

Amazing how this DNA analysis could be made within minutes, too. In reality you have to wait weeks.

So they look into that cop's history, they're especially interested in his financial information. Looks as if he has a secret son. Sure enough they track down a series of checks to who appears to be Hector's mother. Upon visiting her they learn that Hector ran away. 

A voice mail message he leaves for his mother has some noise in the background which can be enhanced by using magic technology. This is how they find out where Hector is hiding.

The rest is history.
Sounds easy enough, right? So I say we just graduated and are amateur investigators as of today, congratulations!
Would you risk tampering with evidence to cover for a family member or friend?
Do you like watching CSI? Who's your favorite character and why?

Thank you for reading, have a wonderful weekend and be sure to check back Monday for the letter G!

Image by Gerd Altmann from Pixabay


  1. I love shows like CSI or Bones, I find it super interesting the level if details they have to work with.

  2. I love shows like CSI or Bones. It's fascinating how detailed their work is. I don't think I'd have the patience!

  3. Although you have to wonder why the cop wrote "Hector-soda can" in his official notebook?

  4. I don't think I would tamper. Too many other related clues to connect which you are not aware of. And removing something might actually be the nail in the coffin.- Erin (http://www.erinpenn.com/blog/)

  5. Very interesting. I love the way you incorporate the TV shows with your examples. Makes perfect sense then.

    Janet’s Smiles

  6. I watched all the CSI shows and at times I would think how stupid do they think we are because I realise things take longer then a few minutes. That said I really liked the post and found it super interesting

  7. The CSI factor has created so many misconceptions in the public's minds. Expectations are really unrealistic. Still, the shows are a lot of fun to watch. It's just important to know that this isn't a documentary. :)
    Financial Help to Avoid Burnout

  8. The schools here have a forensics class. They go over all this sort of stuff. It's popular.

  9. I have a friend who is a fingerprint expert and love hearing her explain about it. But I always think crime show TV requires a canister of salt and should never be considered reality.

  10. So much of the information on TV is bad....I've used DB Lyle's books for research and had retired forensic folks review what I've written. It's so easy to, um, take the easy way out in writing.

    DB McNicol, author
    Microfiction: Flower


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