The couple disappeared during a four-day trip to Catalina Island and
Ensenada, Mexico. The ship returned to Long Beach about noon Friday with its 2,000 passengers, minus the couple, whose names have not been released.
Carnival officials said the couple's cabin door was double-locked from the inside with a "do not disturb" sign on the handle, and the door leading from the cabin to the balcony was unlocked.
The couple's personal belongings were still in the cabin, according to
Carnival. The last time the couple had been seen by the ship's crew was about 7:45 p.m. Tuesday, according to a Coast Guard statement.
Laura Eimiller of the FBI said agents were collecting evidence and had not yet drawn any conclusions about the nature of the couple's disappearance.
"Whether we're dealing with a homicide, a suicide situation or an accidental death," the FBI would not make any determination "until we have all the facts," Eimiller said.
A Coast Guard crew in a C-130 airplane from the Sacramento air station searched the ocean between Ensenada, Catalina Island and Long Beach, but no sign of their bodies were found.