As the fishing vessel Alaska Ranger sank to the bottom of the Bering Sea, crewman Byron Carrillo and 1st Assistant Engineer James Madruga struggled to stay afloat in the rough and frigid waves.

With Carrillo drifting into hypothermic shock after nearly five hours, the arrival of a Coast Guard rescue helicopter was a blessing, Madruga said Friday. He told the rescue swimmer to "take Byron first" and watched the panicked crewman being loaded into a dangling basket.

But when he reached the helicopter himself, Carrillo was nowhere to be seen, Madruga said during the first day of public testimony on the incident before a board of Coast Guard investigators.

Carrillo's disappearance is one of the many unknowns the Coast Guard and National Transportation Safety Board are grappling with as they try to re-enact the Easter Sunday sinking. Five men, including the captain, died in what was one of Alaska's worst fishing accidents in recent memory.

"When I got up to the chopper I asked them, 'Where was the guy they brought up before me?"' Madruga said at the hearing before the Marine Board of Investigation in Dutch Harbor.

According to the Coast Guard, the crew and other survivors told Madruga he was the only one. No other man had been brought up.

"This is the part now where I don't understand," said Madruga, of San Diego. "He took Byron. I saw Byron get into the basket and go up. It was pretty hard to look up because of the wind on your face. And the swimmer came for me, and I went up."

The Coast Guard said it is investigating the loss of an individual from the basket during the rescue, but said that person's identity has not been determined.

In total, the Coast Guard plucked 42 crewmen from the dark waters and Madruga ended his testimony with a nod to the rescue teams.

"You guys are really super, what you did," he said.

The public hearings will continue for approximately two weeks in Dutch Harbor, Seattle and possibly Anchorage, said Coast Guard spokeswoman Sara Francis.