A Willingboro man who stabbed his elderly mother to death and then set her house on fire pleaded guilty to manslaughter and arson charges today that will carry a prison sentence of 28 1/2 years, according to a plea agreement worked out with the Burlington County Prosecutor's Office.

During a hearing in Superior Court this afternoon, authorities said Robert M. Anderson Jr., 49, murdered his mother, Jestie Mims, 70, on Jan. 17 during a heated argument that began when she accused him of stealing her laptop.

They said Anderson bound his mother with duct tape and stabbed her repeatedly with a kitchen knife. He then left her body in a bedroom in the home he shared with her, took cash from her purse and drove her Mercedes to Camden where he bought drugs and "partied."

Over the next two days, with his mother's dead body still in the bedroom, Anderson returned to the home on Maplewick Lane several times, authorities said. On Jan. 19, concerned that his son would be returning from a weekend trip and would discover the body, Anderson used gasoline to set the house on fire, prosecutors said.

Anderson was arrested a day later, in part based on a tip from a motorist who became suspicious after seeing Anderson throw a bag from the Mercedes into a storm drain off Route 130. The motorist, who wrote down the license tag number of the Mercedes, reported the incident to police who found the kitchen knife that was the murder weapon in the bag.

Under the terms of a negotiated plea agreement, authorities dropped a first degree murder charge in exchange for guilty pleas to aggravated manslaughter and aggravated arson.

Anderson has been held on $750,000 bail since his arrest.

Superior Court Judge Jeanne T. Covert scheduled sentencing for Jan. 29.