OLD ORCHARD BEACH (AP) - A 22-year-old college dropout was arrested Friday in the deaths of three family members whose bodies were found in their burned-out home, state police said.

Matthew Cushing was charged with three counts of murder and one count of arson in the stabbing deaths of his mother, Carol Bolduc, 42; his stepfather, Christopher Bolduc, 42; and his half-brother, Joshua Bolduc, 15.

At a news conference, police declined to comment on a motive but said Cushing admitted to the killings. Investigators said a backpack containing a bloody knife and a stun gun was found in Cushing's apartment in Old Town.

According to court documents, there was friction between the Bolduc couple and Cushing because they refused to go along with his plan to leave school to visit a friend in London and go backpacking in Europe.

Police had immediately described the Wednesday night fire as suspicious and the state fire marshal's office said Friday that it was deliberately set.

Investigators said fires were started in the kitchen, hallway and basement stairway of the Cape Cod-style home and a melted plastic gas can was found on the kitchen floor.

Cushing had been staying with relatives in Lincoln County and was arrested after being brought to the sheriff's office in Wiscasset for questioning. He was being held in the York County Jail pending an initial appearance Monday in Superior Court.

Cushing was a student at the University of Maine but had taken the semester off while living in Old Town.

Christopher Bolduc operated two novelty shops near the Old Orchard pier in this summer resort town, which has a year-round population of 9,000. The family lived in a fairly new residential neighborhood near a golf course, and Carol Bolduc was president of the neighborhood association.

Administrators at Old Orchard Beach High School, where Josh Bolduc was a freshman, planned to open the school Saturday to enable students and parents to meet with grief counselors.