(CNN) -- An autopsy has been completed on former Olympian and UNC track coach Antonio Pettigrew, but reports from the examination are pending and the cause of his death has not been released, the North Carolina Office of the Chief Medical Examiner said Wednesday.
The body of Pettigrew, a former 400-meter world champion who returned his gold medal after he admitted doping, was found in the back seat of his car early Tuesday, according to the Chatham County, North Carolina, Sheriff's Office.
Pettigrew, 42, was an assistant track coach at the University of North Carolina. His friends were looking for him after he failed to show up for work, authorities said. "They attempted to retrace his route to work and shortly afterwards found him unresponsive in the back seat of his 2008 white Dodge Aspen on a bridge on U.S. 751."
Deputies responded to the call about 3:15 a.m. "and found he was deceased with no apparent trauma," the statement said. "There were indications that Pettigrew may have taken the sleep aid Unisom, but it is still unclear if this caused his death."
Pettigrew's body was taken to a hospital, and the medical examiner ordered an autopsy, police said. The autopsy was completed Tuesday, said Sharon Artis of the medical examiner's office.
Pettigrew's wife had also reported him missing, and deputies in Wake County had responded to the couple's Apex, North Carolina, home, authorities said. He had last been heard from about 10:30 a.m. on Monday, the statement said.
Pettigrew won gold at the 1991 world championships in Tokyo, Japan, and was a member of the American 4x400 squad that won a gold medal for a relay in the 2000 Olympics in Sydney, Australia.
However, in 2008 Pettigrew admitted being part of a systematic doping program organized by former coach Trevor Graham between 1997 and 2003. Members of the relay squad were stripped of their medals.
Pettigrew was in his fourth season at UNC, where he led the university's sprinters, hurdlers and relay teams, according to the UNC Athletics website.
"Although we are still learning the circumstances, we are deeply saddened to learn of Antonio's death," UNC athletic director Dick Baddour said Tuesday in a statement on the website. "I was particularly impressed with his student-athletes and the pride he took in representing the University of North Carolina. Our deepest condolences go out to Antonio's family, particularly his wife and son."