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Forensics by Kalia and Carolyn

Carolyn's sister Lizzy is celebrating her birthday, but we're investigating a crime. We returned home to find Lizzy's party set-up trashed. The cake was half-eaten, presents were thrown all over, and there was even some bright red stuff dripping off the table. This is clearly a birthday whodunit. Our question: How can we use forensic science to finger the culprit?

What did we do?
There were a lot of possibilities for the bandit: our dad, neighbor, Lizzy, and even a balloon-delivery clown were suspects. We found fiber, saliva, and fingerprint samples at the crime scene, so we gathered hair, saliva and fingerprint samples from each suspect. Then we compared the crime scene evidence to our samples and tried to find a match. We also interviewed all the suspects.

What did we find out?
We found fingerprints at the scene for everybody except the clown, so that didn't narrow things down much. We had a hard time telling the fibers apart under the microscope, but we used a laser pen to estimate the thickness of each fiber. The crime scene fiber didn't match any of our suspects! Lastly, Kalia's cousin helped us with DNA testing for the saliva samples, but the crime scene sample proved to be non-human! After asking questions and recreating the scene, Lizzy confessed to breaking into her presents, but the fiber and DNA evidence pointed to a new and FURRY suspect. It was Sammy the family dog who ate the cake!

What can you do?
  • Practice lifting fingerprints like the CSIs do! Using an artist's paint brush and some dust from a charcoal briquette, apply a light coating of charcoal dust to a surface with fingerprints. Use clear packaging tape to "lift" any prints you see off the glass, then stick the tape onto white paper. You've just captured a fingerprint!
  • Ride your bike through some soft sand, and examine the tire tread pattern that is left behind. How does the pattern change if the tires are under-inflated?
  • One kind of forensic analysis involves splashes and splatters. Fill up some water balloons, and throw them at a dry and level paved surface. What distinguishes the splatter of a balloon that falls straight down, compared to one that hits at an angle?
  • Use this forensics investigation as a science fair project idea for your elementary or middle school science fair! Then tell us about it!
more resources
More on forensic science.

Go to the DFTV Boards, and tell us about your science investigation.
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