Police identified the man as Kyle A. Vanwinkle, 30, of Smithville. They said his cause of death is still unknown after an examination of his body did not show any obvious signs of trauma.
Detectives say it could be another four to six weeks before they receive autopsy and toxicology results, which could help them determine if a crime has occurred.
Three persons of interest, questioned in the case, were released.
Police said Sunday that Vanwinkle was found inside someone else's vehicle in the parking lot at the stadium. Police responded after a struggle, where they found Vanwinkle unconscious.