Expert: Primary compound found in Casey Anthony trunk was gasoline

(CNN) - Chemical testing of air samples from the trunk of Casey Anthony's car primarily showed the presence of gasoline, jurors in Anthony's capital murder trial heard Wednesday.

Other compounds, including chloroform, were also found, but the amount did not appear to be large, University of Central Florida chemist Michael Sigman told jurors in the Orlando courtroom. Testing was not done to determine the amounts, Sigman said, but "they gave very low responses in the instrument."

While some of the compounds found are associated with human decomposition, Sigman told defense attorney J. Cheney Mason, he cannot definitively say that their presence indicated a decomposing body was in the trunk, because there are other natural sources for those compounds as well.

Sigman took the air samples from the trunk, one of which was sent to Arpad Vass at Tennessee's Oak Ridge National Laboratory.

Earlier in the trial, Vass testified that testing on a carpet sample from the trunk showed chloroform at a level that was "shockingly high." He also testified the odor in the air samples he received was "extremely overwhelming." He identified it as human decomposition.

Casey Anthony, 25, is charged with seven counts in her daughter's death, including first-degree murder. If convicted, she could face the death penalty.

Prosecutors allege Anthony used chloroform to render her daughter unconscious, then used duct tape to cover her nose and mouth, suffocating her. Caylee's remains, prosecutors allege, were then put into Anthony's car trunk and eventually disposed of. The girl's skeletal remains were found in a wooded field on December 11, 2008, nearly six months after her family last reported having seen the child.

Defense attorneys say Caylee was not murdered, but that she accidentally drowned in the family pool on June 16, 2008, the day she was last reported to have been seen. They argue that Anthony and her father, George Anthony, panicked and covered up the death. George Anthony has rejected that scenario in his testimony.