Forty-eight-year-old John Gilbert was set to stand trial next week for the murder of Jason Dragos.
Dragos' body was discovered inside a closet at the Burr Ridge trucking company where both men worked.
Prosecutors said Gilbert, who was Dragos' boss, was stressed out at work and was angry because Dragos went over his head.
Gilbert faces 20 to 60 years in prison. He will be sentenced December 20.