ORLANDO, FL --A chemist who collected and tested air samples from the trunk of Casey Anthony's car testified Wednesday that he couldn't say for sure there was ever a body inside of it, statements that conflict with prosecutors' experts. Defense witness Michael Sigman pulled the samples from Anthony's trunk six days after the skeletal remains of Anthony's 2-year-old daughter Caylee were discovered in a wooded area in December 2008. He was one of five witnesses to take the stand as the defense continued to attack the prosecution's contentions that the toddler was suffocated by duct tape and then spent at least some time in the trunk. "I cannot conclusively determine that there were human remains in the trunk," said Sigman, a chemistry professor at the University of Central Florida. Anthony is charged with first-degree murder in her child's death. She has pleaded not guilty and faces a possible death sentence if convicted. The defense says the toddler drowned in her grandparents' swimming pool. Anthony's defense team also called a geologist, toxicologist and fiber analyst -- all from the FBI -- as witnesses on Day 25 of the trial, which was only a half-day because of a prior commitment for Judge Belvin Perry. Sigman's testimony conflicted with research scientist Arpad Vass, a former colleague at Oak Ridge National Laboratory. Vass, a witness for the prosecution, said he determined human decomposition in the trunk based on an unusually high amount of chloroform found on a carpet stain. Prosecutor Jeff Ashton pointed out during his cross-examination of Sigman that by the time he collected his air samples, the trunk's carpet and spare tire cover had been removed. "So your samples only tell you want was in the air, it doesn't tell you where (any gasses) came from, correct?" Ashton said. "Yes," Sigman responded. Ashton also noted that Sigman didn't have the collection instrument Vass recommended and therefore couldn't take a large sample. Sigman only found "traces" of chloroform and a primary presence of gasoline, but Ashton got him to acknowledge the chloroform present could have come from a source other than cleaning supplies like a bottle of bleach. "There's nothing in our results that indicate the source of chloroform...we simply know it's there," Sigman acknowledged. Chloroform or other signs of human decomposition could not be found on any of the clothing from Casey Anthony's closet, or on trash and debris from the trunk, FBI hair and fiber analyst Karen Lowe testified. Lowe also said that of hundreds of hairs collected from items at the Anthony home and inside the car, only one exhibited any characteristics of human decomposition. FBI geologist Maureen Bottrell testified that she analyzed 22 pairs of shoes taken from the Anthony home. She said three pairs of shoes had significant enough amounts of soil to compare with samples taken from the site where Caylee's were found. But she found the soil on those shoes differed. Perry had originally hoped the jury could start deliberations next week, but that timeline will likely be delayed at least a week. The state has already notified him of its intention to call rebuttal witnesses before closing arguments.