A key forensic expert in the Casey Anthony murder trial testified Monday that air samples taken from the woman's car had an "overwhelming" odor of human decomposition.

Dr. Arpad Vass, a researcher at the Oak Ridge National Laboratory in Tennessee, told an Orlando courtroom that compounds present in early human decomposition were detected inside the trunk of Anthony's Pontiac Sunfire.

Anthony, a 25-year-old Orlando mother, is accused of killing her 2-year-old daughter, Caylee, in 2008. She has pleaded not guilty.

Vass, one of the state's key witnesses, has pioneered a novel technique for detecting human decomposition from air samples. 

Vass told the courtroom Monday that he "essentially jumped back a foot or two" upon opening a can containing an air sample from the car's trunk. He said he recognized the odor as human decomposition.

"The odor was extremely overwhelming and strong," he said. 

Vass also testified that a "shockingly high" level of chloroform -- a chemical that can induce unconsciousness -- was also detected from a carpet sample taken from the car's trunk. 

"We have never seen chloroform at that level before," Vass told the courtroom. 

Prosecutors are trying to prove that Anthony suffocated her daughter with duct tape, while Anthony's defense team claims the toddler drowned in her grandparents' swimming pool.

Anthony had previously told investigators she left her daughter with a baby sitter in June 2008, and never saw the pair again. 

If convicted, Anthony could be sentenced to death.

The Associated Press contributed to this report 

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