A 21-year-old Marine lance corporal was arrested last night and charged with killing Shannon Anne McMillan, a legal secretary who was found stabbed to death in her Silver Spring apartment on Oct. 5, Montgomery County police said.

Police identified the suspect as Arnold Jason Williams, who lives at 3302 Hampton Point Dr. in the same Hampton Point North complex to which McMillan had moved in September. Police said Williams had known McMillan, whose partially clothed body was found in her third-floor apartment at 3318 Parkford Manor Ter. by a boyfriend who had been unable to contact her.

Police said at the time there was no sign of a struggle in the apartment. Investigators would not comment last night on a possible motive.

Police said Williams, who had been questioned earlier during the investigation of McMillan's slaying, was arrested after a second round of questioning last night in the Wheaton police station.

Williams became a suspect as a result of interviews with every occupant of McMillan's apartment building, police said.

Williams, whose Marine Corps assignment was to the corps barracks in Southeast Washington, was held without bond on a first-degree murder charge.

McMillan was a legal secretary at the firm of Reed, Smith, Shaw & McClay in McLean. She moved to the apartment in Silver Spring from Annandale.