Pettigrew was crowned world 400m champion in 1991
Former 400m world champion Antonio Pettigrew has been found dead at the age of 42 in the United States.
Pettigrew was a member of the US 4x400m relay team at the 2000 Olympics, but was subsequently stripped of his gold medal after he admitted doping.
A North Carolina police official told BBC Sport Pettigrew was found in his car with sleeping pills next to him, although no foul play is suspected.
Pettigrew was working as a coach at the University of North Carolina (UNC).
"We are deeply saddened to learn of Antonio's death," said UNC athletic director Dick Baddour.
"I was particularly impressed with the relationships he established 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."
The apparent circumstances of Pettigrew's death were explained by Major Gary Blankenship, of the Chatham County Sheriff's Office.
"It is unclear what happened but his body was found at 0315 local time on Tuesday in the back seat of his car parked by the side of a thoroughfare in our county," he told BBC Sport.
"There was a sleep aid [sleeping pills] next to his body. We don't know if he took them accidentally or intentionally."
He added: "No foul play is suspected. We won't find be able to confirm what happened until we find out the results of his toxicology report, which will take a few weeks."
Police said in a statement that an autopsy was ordered by the local medical examiner and Pettigrew's body was transported to UNC Hospital.
Pettigrew won the 400m at the World Athletics Championships in Tokyo in 1991.
He also won golds while making up part of the 4x400m relay teams at the 1999 and 1997 world championships in Seville and Athens.
However, Pettigrew voluntarily surrendered those medals after admitting in 2008 that he had used performance-enhancing drugs between 1997 and 2003.
That led to the British quartet of Roger Black, Jamie Baulch, Iwan Thomas and Mark Richardson, who had finished second in the 1997 race, being named winners.
The US team of Pettigrew, Chris Jones, Tyree Washington and Jerome Young had edged out the British team by 0.18 seconds. In May 2010, Black, Baulch, Thomas and Richardson were formally handed their gold medals.
Pettigrew and the rest of the 2000 Olympics 4x400m team - Michael Johnson and brothers Alvin and Calvin Harrison - were stripped of their golds by the International Olympic Committee.
The drugs scandal also led to a two-year ban for Pettigrew.
The admission by Georgia-born Pettigrew about taking the substances had been made during the trial of former coach Trevor Graham, who was later found guilty of perjury.
The court in San Francisco heard Pettigrew testify that Graham had encouraged him to inject the banned substances EPO and human growth hormone.