Sep 16, 2008 10:55 pm US/Central
Tiny Pieces Of Evidence Could Lead To Big Break
(WCCO)
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The blue dot is a period on a business card, and the red are the paint chip layers that the Bureau of Criminal Apprehension is examining under a microscope.
CBS
Investigators hope to know more on Wednesday about the hit-and-run death of a Minnesota man. Jim Nisser died last week less than a block from his work at Minikahda Country Club. The car that hit him while he was riding his bike took off, but left behind some paint chips.
Some of those chips were sent to the Minnesota Bureau of Criminal Apprehension (BCA) for analysis. Investigators hope any information the scientists can find will help them find whoever hit Nisser.
Susan Gross heads up the BCA trace lab with three other people. They analyze glass, hair, fibers, shoe prints, paint and much more. She couldn't discuss Nisser's case, but could discuss how she examines the chips.
First, she puts chip under a microscope and cuts off a small piece to analyze the layers of paint. Gross said she can work with paint chips as small as a pin's head, but prefers larger samples.
"Automotive paint has more than one layer, typically there's at least three layers," she said.
She then sends the paint piece through an infrared laser to determine what components make up each layer of paint. From there, she enters the ingredients into a database of more 14,000 types of cars in the U.S. and Canada.
The BCA obtains access to the database by sending in 50 known samples of paint. Every summer, Gross and her colleagues go to the junkyards to collect the samples.
Once the information is entered into the database, the computer spits out a list of possible matches. Eventually, Gross can whittle that number down through process of elimination. For example, if the list shows the top layer has titanium oxide and Gross knows it doesn't, she can exclude that match from the list.
"I've had ones that I haven't found any matches. I've had ones that I can narrow it down to a foreign vehicle," she said. She said sometimes the paint chips are too small or the car isn't in the vehicle database.
Gross said she has never been able to match a make and model, but points out, her office does very few analyses where she works with only unknowns.
(© MMIX, CBS Broadcasting Inc. All Rights Reserved.)
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