WAUKEGAN, Ill. (AP) — A northern Illinois man has pleaded guilty to first-degree murder in last year’s slaying of his girlfriend’s 5-month-old son. The boy was never found.

The Lake County State’s Attorney’s office says in a news release that prosecutors agreed with Tuesday’s plea to seek a sentence for Demetrius Thorpe that is no longer than 35 years in state prison. Thorpe returns for sentencing on Sept. 2.