Joe Burbank/Orlando Sentinel/MCT/Getty
06/22/2011 at 02:30 PM EDT
The air in Casey Anthony's car trunk contained chemicals associated with human decomposition but that didn't conclusively prove a body was in there, a defense witness testified Wednesday at her murder trial.
Dr. Michael Sigman, a chemistry professor at the University of Central Florida, testified the trunk of Casey's Pontiac Sunfire showed traces of gasoline, chloroform and other chemicals.
Although associated with human decomposition, the chemicals also are linked to onions, cabbages and Clorox, and the compounds "gave very low responses," said Sigman.
As a result, he told defense attorney Cheney Mason, "I cannot conclusively determine ... that there had been human remains in the trunk of the car."
Prosecutors in the murder trial in Orlando had called several experts who concluded that based on the air samples, a strand of hair, insect activity
and the reaction of cadaver dogs
that a body was in fact in the Florida mom's car.
Casey, 25, who faces the death penalty if convicted in her 2-year-old daughter Caylee's death, busily passed notes to her lawyers throughout the morning's testimony.
Among several other witnesses who took the stand was Madeline Montgomery, a forensic toxicologist for the FBI.
She testified that she found no evidence of drugs – including calming medications Xanax and Valium – in hair presumed to be Caylee's. But she also acknowledged she could not test the hair for chloroform.