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Inside Tucson's Crime Lab: Arson

How investigators identify fire accelerant
Posted: 6:30 AM, Dec 04, 2019
Updated: 2019-12-04 08:31:35-05
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TUCSON, Ariz. — When Tucson police arrive at an arson like the one involved in the Susan and Blane Barksdale murder case, crime scene investigators comb the scene for clues. They pick up the pieces and after checking it into evidence lockup it ends up at the TPD crime lab. Fire debris analyst Lisa Windsor will test the evidence to find out if someone used an accelerant to start a fire at a crime scene.

"My job is to analyze fire debris evidence like carpet or seat cushions or curtains, tile flooring or a liquid for the presence of of an ignitable liquid. I look for flammable liquids such as gasoline or acetone or combustible liquids like diesel fuel or charcoal lighter fluid," Windsor said

Windsor also says police have to keep a tight lid on evidence literally. They use paint cans, mason jars and buckets all the way up to a 10 gallon drum for storage. Both old school and state of the art techniques are used to test the evidence that can come in at any size.

"It needs to be airtight because fire debris evidence can easily evaporate away so so it needs to be put away in some sort of airtight container. Carpet samples can fit in here there's sometimes clothing items. We've had different types evidence like a piece of drywall. We typically we'll get 30 to 40 cases per year," Windsor said.

The process for testing is simple in some ways and complicated in others. Windsor puts a small piece of evidence into a mason jar. It's placed into a machine called a gas chromatography mass spectrometer. The instrument will process the charcoal strip and solvent to determine if flammable elements are on that evidence.

"What I will do is place the jar inside of an oven and ill heat it up overnight on a low temperature. The purpose of me heating up the evidence is because if there's any ignitable liquids trapped it within that debris. That vapor is attracted to the charcoal strip," Windsor said.

After heating the evidence its removed from an oven, cooled and analyzed all the way down to the element. It can take up to 2 days to get results.

"I take half of the strip that's used in the analysis the other half of the strip is saved for a secondary analysis if there is a need for one," Windsor said.

Once testing is complete, its double checked and results are released to detectives then its on to court as investigators work to close their case.