Casey Anthony Trial: Witness Rebuts Human Decomposition in Car's Trunk

VIDEO: The defense picks up steam, calling in witnesses to undermine the prosecution.
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A forensic chemist testifying in the Casey Anthony trial said today that the car belonging to the Florida mom accused of murdering 2-year-old daughter Caylee did not test positive for human decomposition.

Michael Sigman, a chemist at the National Center for Forensic Science, said that air samples from Casey Anthony's car trunk tested positive mainly for gasoline. Chloroform and two other chemicals were present.

"I could not conclusively determine that the presence of those compounds indicated that there had been human remains in the trunk of that car," Sigman told jurors.

Casey Anthony, 25, is accused of murdering Caylee in the summer of 2008. She could face the death penalty if convicted.

The prosecution has argued that Caylee died from chloroform and duct tape placed over her nose and mouth. The defense argues that she actually drowned in the family pool on June 16, 2008, 31 days before she was reported missing.

Sigman's testimony casts shadow over the prosecution's star witness, Dr. Arpad Vass. Vass testified earlier this month that the trunk of Casey Anthony's car had an abundance of chloroform, a sign of human decomposition and a chemical that also can be used to commit murder.

Evidence photos in Casey Anthony murder trial

Sigman originally collected air samples from the Pontiac Sunfire's trunk in July 2008. One of his air samples was sent to Vass to analyze. Sigman then analyzed another sample on his own.

"The results of that test were consistent with the presence of gasoline," Sigman said.

Sigman collected five more air samples from the car's trunk using different methodologies to concentrate the sample. Those samples showed gasoline, chloroform and two other chemicals.

Sigman said chloroform is frequently found in bleach.

Casey Anthony Trial Sticks to Forensics

Upon cross examination, Sigman said that the methodologies he used to analyze the samples was not as good as the method used by Vass.

Sigman used tedlar bags to collect air samples. He also collected samples using two other methodologies in an attempt to concentrate the samples to gain a better reading. Those methods were the collection of solid phase microfiber samples and the use of activated carbon strips.

Vass's results came from the use of a triple sorbent trap.

Along with the sample sent to him from Sigman, Vass also reviewed samples from the carpet of the trunk. When he opened a can containing a sample from the car's trunk, he was struck by the odor.

"I essentially jumped back a foot or two…I was shocked that that little itty bitty can could have that much odor associated with it…I would recognize it as human decomposition," Vass told jurors on June 6.

Vass works at the Oak Ridge National Laboratory in Tennessee where he analyzes the odor of death by working with cadavers at a "body farm."

Vass said that chloroform is normally found in trace amounts, in parts per trillion. The trunk sample showed chloroform in the parts per million range, significantly higher than the average.

Upon cross examination, Sigman told prosecutors that Casey Anthony's trunk did smell, but because he doesn't study human decomposition, he couldn't say the car reeked of death.

During today's abbreviated hearing, the defense continued to focus on scientific evidence.

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