A couple was found dead Thursday in an apparent murder-suicide aboard a Holland America cruise ship that docked in Puerto Rico, officials said.

The unidentified man and woman were in their 50s and from Cleveland, Ohio, police Sgt. Ricardo Cruz told The Associated Press.

Cruz said blood was found in the cabin aboard the Ryndam, but it was unclear how the couple died. "We don't know yet whether an object was used or what the motive was," he said.

He said the ship's crew found the bodies when they checked on the couple after not seeing them for a while.

The FBI has taken over the investigation.

It was unclear exactly when the couple died. The ship departed Tampa, Florida, on Sunday for a two-week cruise in the southern Caribbean. It stopped in Key West on Monday and then spent two days at sea before docking in historic Old San Juan on Thursday, Holland America spokesman Erik Elvejord said.

"We are terribly saddened by this tragic event," the company said in a statement.

Cruise ship passengers said they were not aware of what had happened.

"This is a shock to me," said Mark Moore of Watertown, New York, who was traveling with his wife.

He said the crew had roped off part of the ship and hung a sheet in the hallway as passengers disembarked around noon.

The Ryndam was scheduled to depart Puerto Rico late Thursday and arrive in St. Thomas on Friday.