MIAMI BEACH, Fla. (AP) — The Coast Guard said Thursday that it had found four additional bodies in its search for dozens of migrants lost at sea off Florida but that it would call off its active search for survivors at sunset if it doesn’t receive any new information.

Homeland Security Investigations officials said they were actively investigating the case as a human smuggling operation.

Authorities have now found a total of five bodies, leaving 34 missing.

Coast Guard Capt. Jo-Ann F. Burdian said the decision to suspend the search at sunset Thursday, pending any new discoveries, was not an easy one.

“We have saturated the area over and over over again,” she said. “We’ve had good visibility. We know we’re searching in the right area. We’ve overflown the vessel a number of times and have found additional deceased persons. It does mean we don’t think it’s likely that anyone else has survived.”

The Miami office of Homeland Security Investigations said it believes the overturned boat to which a man was found clinging on Tuesday was part of a human smuggling operation and they have launched an investigation to determine who was behind it. Under federal law, a smuggler convicted of causing a death is eligible for execution.

“The goal of this investigation is to identify, arrest and prosecute any criminal or criminal organization that organized, facilitated or profited from this doomed venture,” said HSI Miami Special Agent in Charge Anthony Salisbury.

The lone survivor was found hanging on to the 25-foot vessel about 40 miles off Fort Pierce, Florida. He told a good Samaritan and authorities that the boat capsized late Saturday after he and 39 others had set out for Florida from Bimini, a chain of islands in the Bahamas about 55 miles east of Miami.

Authorities said the boat was found about 100 miles north of where it capsized, apparently pushed north by the Gulf Stream, a warm, swift current that wraps around the Florida peninsula and flows north along the Atlantic Coast of the United States. No one was wearing a life jacket, the rescued man told authorities.

The turbulent waters of the Gulf Stream can be treacherous even on a calm, sunny day. Throw in an overloaded boat, inexperienced mariners, stormy weather and the dark of night, and they can become deadly.

A small craft advisory had been issued as a severe cold front blew through the dangerous passage on Saturday and Sunday, with winds up to 23 mph and swells up to 9 feet. Tommy Sewell, a local fishing guide, said there were high winds and fierce rain squalls from Sunday into Monday.