Twenty four-year-old jockey Michael Baze was found dead in his vehicle in the stable area of Churchill Downs on Tuesday afternoon.
Witnesses said Baze parked in the lot around 2:30 a.m. in the morning and his Cadillac SUV had been sitting there idling all morning until someone called 911.
"There doesn't appear to be foul play," ABC News quoted Louisville Police spokeswoman Alicia Smiley as saying. "But we are awaiting the coroner's report and autopsy. This is a death investigation as opposed to a homicide."
His agent Bob Kelly said Baze sent him a text the evening before and they had planned to meet at 6 am on Tuesday. He tried calling and texting him that morning.
The Daily Racing Form reported that Baze was the leading jockey at Arlington Park last summer. In February he rode Nehro to victory at Oaklawn in the Louisiana Derby. Nehro, with a different jockey aboard, was second in Saturday's Kentucky Derby.
"This winter, he rode at Oaklawn, had 34 wins, had a very good meet, including a couple of stakes wins," the Los Angeles Times quoted Churchill Downs spokesman John Asher as saying.
Baze recently lost a mount after showing up drunk, and ESPN reported that he was scheduled for a preliminary hearing Thursday on charges of possession of cocaine, dating from November.
Baze's father, an uncle and cousins were also jockeys.
"To me, he was one of the premier riders in the country, as far as me watching every day," ESPN quoted jockey Gary Stevens, who is a relative by marriage, as saying. "And there's no bias there; the kid could just flat ride. I think he was just starting to get the notoriety and the respect from the horseman."