ESCANABA, Mich. (AP) — A woman has pleaded guilty to torturing and abusing her son who was kept inside their home in Michigan's Upper Peninsula for four years.

The guilty plea came Thursday in Delta County after the woman waived her right to a key hearing to determine whether there was enough evidence for a trial.

The woman's boyfriend is expected to make a similar guilty plea later Thursday.

Police in Escanaba say the 15-year-old boy was kept inside the Escanaba home for four years, rarely leaving a room made from tarps while being tortured and abused. He was removed by officers in April.

The boy's mother and her boyfriend have been held in jail since the discovery.