SAN FRANCISCO (AP) — The U.S. Coast Guard said Tuesday that it has suspended the search for a man believed to have gone overboard from a cruise ship as it was returning to San Francisco after a voyage to Ensenada, Mexico.

The Ruby Princess, operated by Princess Cruises, arrived in San Francisco at 6:50 a.m. Monday following the five-day trip. Officials searched the ship several times for the missing passenger, according to a statement released by the cruise line. They also scoured security videos, but there was no sign of the man, a 72-year-old American citizen traveling alone, the statement says.

“Having ruled out other possibilities, this is being treated as a man overboard incident,” Princess Cruises said.

The Coast Guard began aerial searches Monday afternoon in the Pacific Ocean about 45 miles (72 kilometers) off the coast of Monterey, California. The effort was suspended around 5:30 p.m. “pending any new developments,” Coast Guard Petty Officer Loumania Stewart said in an email Tuesday morning.

U.S. Customs and Border Protection was investigating the disappearance.

The Ruby Princess left San Francisco again Monday evening for a 16-day voyage to the Hawaiian Islands.