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How Do Investigators Match Paint Chips To Cars Involved In Crimes?

MINNEAPOLIS (WCCO) -- Jose Hernandez Solano died Thursday after spending 12 days on life support.

He had been hit by a car in St. Paul while riding his bike on his way home from work on Nov. 26.

Through surveillance video, witnesses and paint analysis from the Minnesota Bureau of Criminal Apprehension, investigators now believe the vehicle that hit Solano is a 2008-2010 metallic sage green Hyundai Santa Fe.

So, how does the BCA match paint chips to cars?

Sometimes, the evidence is left on the road. In other cases, it can be a tiny piece on a victim's clothes.

The trace laboratory at the BCA can analyze a paint chip smaller than a millimeter.

Cross Section Of A Paint Chip
(credit: CBS)

When the evidence comes to the BCA, it is catalogued and sent to a search room. In that room, someone will scrape the clothing to remove any debris. That debris is then put under a microscope and any paint chips found in there are removed.

From there, the paint chip is sliced so scientists can see the four levels of paint most often found in automotive paint: the top layer, the color layer and two bottom layers of primer.

BCA Forensic Science Supervisor Susan Gross works on these types of hit-and-run cases. Her lab generally sees one to three a year.

"It takes a lot longer than you see on CSI. It's not just run it, put it in the instrument and you get your answer," Gross said. "There's a lot of legwork."

Gross could not discuss the Solano case, but did put together a sample paint chip to demonstrate the process for WCCO.

She took the sliver of paint chip and analyzed each of the four layers of paint via computer. Each layer showed her the types of components used in the paint, which she could then put into a database. The database has 21,000 vehicles and 81,000 layers of paint.

In each case, she and the five other scientists in the trace lab come up with any number of possible vehicle matches. Sometimes it's two, other times it's five. If it is anything more than thirty, she says it's not helpful to investigators.

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