Understanding Trace Evidence

This is the last post in my Forensics series for this A to Z Challenge. I’ve had fun with these and I hope they’ve helped you identify some elements of plot you could include in your novels, whether they be in the crime genre or not.

We’ve already covered part of Trace Evidence in previous posts as Fingerprints and Marks and Impressions both are part of this style of evidence. So, what’s left?

Dr. Edmond Locard, a forensic science pioneer, had a theory that became known as Locard’s exchange principle:

“Every contact leaves a trace.”

Unless you move around in a fully protective space suit, you’re likely to leave trace evidence wherever you go. Be it, fingerprints as you open doors, or handle a glass for your drink, or the impressions your feet leave walking across a freshly weeded garden.

What if you then went into someone’s home and deposited the soil on their kitchen floor. You could have also walked through a freshly painted floor and a combination of the two are left in the kitchen. When the police arrive to investigate the case of the stolen cookies, you are likely to incriminate yourself through the trace on your shoes.

And, if your cookie stealing, mud spreading villain broke a window to steal those delicious treats, then they could well have glass shards caught in their clothing, footwear and about their personage. Whilst most of these fragments would work loose within hours, it could still be an avenue for your detective to investigate.

When the case is slightly more serious than stolen cookies, and a struggle, possibly violent struggle has taken place then other evidence will be left behind. One of the most common will be hair.

Dog hair (top) cat hair (bottom) under a micro...

Dog hair (top) cat hair (bottom) under a microscope (Photo credit: Wikipedia)

As well as the possibility of obtaining a DNA sample, hair can be examined to show the species it originated from. That walk in the park with the dog, could be a pointer to whodunnit in your novel, so could the cat hairs deposited from around your criminal’s ankles where their cat rubbed up against them waiting for breakfast.

You also have other fibres. The most common one will be either clothing or carpets. Did your killer put their victim in the boot of their car? Well fibres from the boot are likely to be present when your detective finds the body. That and the blood traces found inside the boot will take some explaining.

If every contact leaves a trace then think about how your criminal arrived at the scene, what interaction they had whilst they were committing the crime and what they could have left behind for your detective and crime scene characters to find.

I hope these posts have stimulated some crime writing ideas for you or things to think about when you decide to break the rules and go for that extra cookie in the middle of the night. πŸ˜‰

Happy Crime Writing!



This is my U post for the A to Z Blogging Challenge. A list of all my A to Z Blogging Challenge posts are to be found here.

Today my photographs are from Universal Studios L.A from back in 1990.

Yes, the ACTUAL clock tower from Back to the Future films.

Yes, the ACTUAL clock tower from Back to the Future films.

I couldn't see if Norman Bates' mother was in the window of the Psycho house

I couldn’t see if Norman Bates’ mother was in the window of the Psycho house

A bit of action from the Miami Vice show. This dates when I went doesn't it? Remember, it was 1990.

A bit of action from the Miami Vice show. This dates when I went doesn’t it? Remember, it was 1990.

About Pete Denton

I'm a writer working my way through the redrafts of a British crime novel. I also write short stories, flash fiction and some screen writing. Check out my blog for more.
This entry was posted in A to Z Blogging Challenge, Writing and tagged , , , , , , , , . Bookmark the permalink.

20 Responses to Understanding Trace Evidence

  1. noelleg44 says:

    Sorry I could not connect with your blog today – enjoyed your post. Haven’t gotten into seriously minute trace evidence yet, but I’m pretty sure it will play a role one of these days! Noelle

  2. bronbloxham says:

    Yup… once again, confirmation that I will need that latex onesy for my impending life as a criminal mastermind! πŸ™‚

  3. Very interesting, and most certainly helpful. I kill and torture characters, so this is good information. πŸ™‚

  4. ocdreader says:

    Too bad we can’t see if mama bates is in the window, though I guess it is kind of creepier not being able to see her…

  5. Julie says:

    It’s amazing what they can find through hair and fibres. They probably go through a lot of sinks and shower drains too. We took our kids to Universal Studios when they were young, and I would love to go back.

    • Pete Denton says:

      It is amazing what they can find. Technology and science are great πŸ™‚

      Universal was fabulous. I’d love to return and see what’s stayed the same and what is new. They had the Star Trek show as well, which was great fun. I hope you manage to get back and enjoy it all over again πŸ™‚

  6. Ana says:

    Great photos of Universal Studios! I’ve been there a few times and always enjoyed it. Was the ET ride there when you went?

  7. EllaDee says:

    I saved the link a week ago but forgot to comment – http://www.canberratimes.com.au/technology/sci-tech/a-hair-could-be-the-clue-to-what-a-suspect-looks-like-20130423-2icp6.htm – “Police could soon use DNA from a single stray hair from a crime scene to determine whether a suspect is bald, has a cleft chin, or skin covered in moles.University of Canberra researcher Dennis McNevin said new techniques being developed could lead to police using DNA to create photofit images of suspects…”
    Your posts have had me taking an interest in things that would usually pass me by…

    • Pete Denton says:

      Happy to help. Or to hinder, whichever it may be πŸ™‚

      It is fascinating what scientists can work out from a mere strand of hair or other item a criminal leaves behind.

  8. Kourtney Heintz says:

    Very intriguing stuff. And important info for mystery/thriller writers. πŸ™‚ I think you would love the Killer Nashville conference: http://www.killernashville.com

    Last time I was there I learned about lock picking, search and rescue dogs, and blood spatter. They even had a faux murder scene set up for us to “investigate”. Going again in August. If you want to plan a trip to the states, come in August. πŸ˜‰

    • Pete Denton says:

      Nashville wouldn’t necessarily be on my list of places to visit, until now!

      I think once I’ve been to a few festivals I’m going to be addicted to them. I hope I can find something similar over here.

      Thanks for the link πŸ™‚

  9. Pingback: The A to Z Challenge and what is a Blog Blitz? | Pete Denton - Writer

  10. My grandfather Albert Gaynor created the clock tower. Check out the screen credits for the movie.

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