Maywood, IL- A horse trainer from Wisconsin was found dead of carbon monoxide poisoning Wednesday in his trailer at Maywood Park racetrack, officials said.

Robert Nevel, 71, of Richland Center was pronounced dead at 11:40 a.m. Wednesday in Loyola University Medical Center in Maywood, according to the Cook County medical examiner’s office. His death was ruled an accident.

Nevel drove to Maywood on Tuesday to watch his horse Big Spiel compete in a harness race, according to his longtime partner, Charm Klebesadel. When Nevel didn’t return home as scheduled, his relatives called authorities. Nevel was found inside his trailer by a racetrack security guard Wednesday.

Representatives of Cook County sheriff’s office, which handled the investigation, were unavailable for comment. Relatives think a propane tank, used for heating, may have leaked or malfunctioned, Klebesadel said.