A 31-year-old Rockland man pleaded guilty Thursday in federal court to making a false distress call to the Coast Guard, resulting in fruitless search for a sinking vessel in December.

Nathan Libby pleaded guilty June 3 in U.S. District Court in Portland to calling in a false distress call. He faces up to five years in prison and a $250,000 fine if convicted. He will be sentenced at a later date.

An affidavit filed in court by Coast Guard Investigative Service Special Agent Mark Root detailed the investigation that led to the charge against Libby.

The Coast Guard received a mayday call on VHF channel 16 shortly after 6:30 a.m. on Dec. 3, 2020. The unidentified man said the boat he was on had lost its rudder and was taking on water, and that the pumps were not keeping up with the water coming in.

The man said there were three people aboard the boat, and they were in Spruce Head Harbor trying to get to the Atwood float.

Marine Patrol Officer Nicholas Stillwell responded to Atwood Lobster Co.’s wharf on Spruce Head Island in South Thomaston and boarded a private vessel in an attempt to locate the boat. No vessel was located.

The Coast Guard sent out a vessel that searched for more than four hours, and a helicopter from Coast Guard Air Station Cape Cod spent more than five hours in the search. Maine Marine Patrol and private boats also participated.

Stillwell returned to the dock and spoke to Libby, a dock worker at the neighboring Spruce Head Fisherman’s Co-op. Libby provided the Marine Patrol officer with a list of boats that went out that morning.

The officer then spoke to someone else at the co-op and played the recording of the distress call. That person said the voice sounded like Libby. The officer went back and spoke to Libby, who said he had heard the distress call. He also acknowledged the co-op office had a VHF radio, which was turned to channel 16.

The officer taped Libby, and his voice was compared to the distress call by an associate research professor at the Language Technologies Institute School of Computer Science at Carnegie Mellon University in Pittsburgh. Associate Professor Rita Singh concluded the voice on the distress call was Libby’s, the affidavit said.

Surveillance video showed Libby was at the co-op office at the time the distress call was made. A check from a radio tower showed the call came from the direction of the co-op.

The fake distress call was made less than two weeks after the Portland-based fishing boat Emmy Rose sank off the coast of Massachusetts, killing its four crew members.