A 22-year-old college dropout was arrested yesterday 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. Cushing was a student at the University of Maine but had taken the semester off while living in Old Town.

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

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.