A hair and fiber investigator for the FBI took the stand as the murder trial of 25-year-old Casey Anthony enters its fourth week in central Florida.

Stephen Shaw told jurors Monday in Orlando that he analyzed hair found in the trunk of Anthony's car and samples taken from 2-year-old Caylee Anthony's skull, which was found in a wooded area.

Shaw testified he saw more evidence of decomposition on the hairs taken from the child's skull than on the hair found in Anhony's trunk.

Prosecutors believe Anthony suffocated her daughter with duct tape. The defense contends the toddler drowned in her grandparents' swimming pool.

Anthony has pleaded not guilty and faces the death penalty if convicted.

Jurors have heard from witnesses ranging from Anthony's family members and friends to forensics experts.