Thomas Lee, 46, suffered fatal head and chest injuries after he fell more than 40 feet Tuesday while taking apart the Splash Water Falls ride at Six Flags Great America, The Chicago Tribune said.

"We don't know how he fell," said Bob Heraver, battalion chief for the Gurnee, Ill., Fire Department. "Nobody really saw exactly what happened until it started to happen. We don't know if it was a slip, a trip or something that gave way."

Heraver said a harness was found attached to Lee's body but it was unclear if it had been properly secured while he was working.

Lake County Coroner Richard Keller says the U.S. Occupational Safety and Health Administration is investigating Lee's death to see that appropriate safety measures were in place at the time of the incident.