Carnival Elation at the San Diego Cruise Ship Terminal

Carnival Elation at the San Diego Cruise Ship Terminal (July 16, 2009)

The FBI arrested a cruise ship passenger Thursday on suspicion of murdering his wife in their cabin during a five-night trip to Cabo San Lucas.

Robert McGill, 55, of Winnetka, Calif., is accused of killing his wife, Shirley, on Tuesday night aboard the Carnival Elation. The ship was on the return leg of a five-night cruise to Cabo San Lucas, when crewmembers were sent to the couple's cabin to investigate a domestic disturbance. They found the body of the 55-year-old woman in the cabin and detained her husband in the ship brig. A passenger who had a cabin close to where the woman died told Fox 5 that security guards were posted outside the door from Tuesday night until the ship arrived at the San Diego Cruise Ship Terminal on Thursday.

Keith Slotter, the special agent in charge of the FBI's San Diego office, said 20 agents traveled out to the ship aboard a Coast Guard cutter Wednesday night while it was at sea and questioned the man. They also interviewed dozens of other passengers. McGill was arrested , Slotter said.

They did not reveal Shirely McGill's cause of death or a possible motive for the killing.

The Elation was scheduled to leave San Diego at 4 p.m. Thursday on another cruise.