Cormorants dry their wings after diving in the Bosphorus River on a warm day in Istanbul on Aug. 23, 2017. In Maryland, police said a shotgun was fired several times from a boat outside Baltimore, killing several birds, including a federally protected gull and a double-crested cormorant. (Ozan Kose/Agence France-Presse/Getty Images)

Prosecutors lack evidence to pursue criminal charges against a Maryland police officer and two companions implicated in the shootings of federally protected birds outside Baltimore this summer, authorities said Tuesday.

“At this point, the investigation is at a standstill,” said Adam Lippe, an assistant state’s attorney in Baltimore County.

Investigators said the shots were fired from a boat near the Key Bridge on July 21, but Lippe said authorities are unable to conclude which of the three occupants of the boat was responsible. Police also said that shots were fired near the Spirit of Baltimore dinner cruise ship, which was taking passengers on a tour.

Lippe said the investigation remains open.

Michael Davey, an attorney for the officer, said it is his understanding that his client will not face criminal charges.

He declined to discuss the case further.

Authorities have not identified the officer, who had been on administrative leave. Lt. Kevin Ayd, a spokesman with the Maryland Transportation Authority police, said on Tuesday that the officer’s arrest powers have been restored.

The incident occurred on the Patapsco River just outside Baltimore. Police said a shotgun was fired several times from a boat, killing several birds, including a federally protected gull and a double-crested cormorant.

The boaters were detained by Baltimore police officers assigned to the marine unit that chased them from the Key Bridge, which crosses the Patapsco River to a creek in Baltimore County. City officers led the investigation, which is being prosecuted from neighboring Baltimore County, where the 21-foot boat was stopped. Maryland Natural Resources Police and the U.S. Coast Guard also responded.

Authorities said an observer aboard a city helicopter saw someone on the boat throw a long gun into the water.

Divers recovered the weapon. Police said they found 210 rounds of shotgun ammunition, 50 rounds of 9mm ammunition, 100 rounds of 5.7mm ammunition and 12 rounds of .22-caliber ammunition on the boat. The speech of all three occupants of the boat was slurred, and empty beer cans were in the craft, police said.