|Pettigrew's Olympic coach said the athlete 'impacted thousands of lives' [GALLO/GETTY]
Former world 400 metres champion Antonio Pettigrew was found dead on Tuesday.
Pettigrew, who is survived by his wife and son, had been an assistant athletics coach at the University of North Carolina for four the past four seasons.
"Although we are still learning the circumstances, we are deeply saddened to learn of Antonio's death," Dick Baddour, the school's athletic director, said of the 1991 world champion.
"I was particularly impressed with the relationships he established with his student-athletes and the pride he took in representing the university."
The 42-year-old Pettigrew, who was stripped of an Olympic gold medal after admitting to doping, was found unresponsive by friends in the back seat of his vehicle in Chatham County in central North Carolina early on Tuesday.
Pettigrew helped the United States win the 2000 Olympic gold medal and three world titles in the 4x400 metres relay but relinquished the Olympic gold and two of the world relay medals after admitting to using performance-enhancing substances.
He competed in one Olympics, the 2000 Sydney Games, during his long career.
A five-times US 400 metres champion, he was honoured in 2000 by the sport's US governing body for humanitarian work.
"He will not only be remembered for his accomplishments on the track but for the thousands of lives his success impacted," 2004 Olympic men's coach George Williams, Pettigrew's coach at Raleigh's Saint Augustine's College, said in a statement.
"He was a role model and mentor who will be sorely missed."
County officials said there were indications Pettigrew may have taken a sleep aid but were unclear if that caused a role in his death.
"Chatham deputies and (emergency management services) arrived and found Pettigrew was deceased with no apparent trauma," Chatham County officials said in a statement.
A spokeswoman for the state Chief Medical Examiners office told the Reuters news agency that an autopsy was incomplete.