CHICAGO (CBS) — An investigation is under way after an inmate was found dead in a cell at the Lake County Jail in Waukegan.

The unidentified 31-year-old man was found alone in his cell on Wednesday morning in a maximum security section of the jail.

The sheriff’s office says the man was arrested  in July and placed in maximum security because he was threatening other inmates, according to a Lake County Sheriff news release.

Last month, a judge ruled the man was unfit to stand trial on burglary and disorderly conduct charges, according to the news release. He was ordered held until the Illinois Department of Human Services determined appropriate placement and treatment.

An autopsy was scheduled for today to determine a cause of death. The Lake County Major Crimes Task Force is handling the investigation.