Three Somali men pleaded guilty Friday to piracy for their roles in the hijacking of a yacht, providing the most detailed description yet about what happened in the days leading up to the shootings that killed the four Americans aboard.

During hearings in federal court, two of the men also pleaded guilty to hostage taking resulting in death. Those men were considered leaders among the crew, with one of them the commander of the pirates' boat when it left Somalia, and the other serving as a negotiator aboard a US Navy ship.

Each of the three men could face mandatory life sentences, although they struck deals with prosecutors that could allow them to receive lighter sentences and eventually be deported to Somalia. They're expected to help prosecutors build their case against the three men suspected of shooting the Americans, and against a negotiator who was based in Somalia and is considered the highest-ranking pirate the U.S. has ever captured.

"Modern piracy isn't swordplay and derring-do; it's armed robbery and cold-blooded murder at sea," FBI Assistant Director-in-Charge Janice K. Fedarcyk said in a statement. "The FBI remains determined to see pirates brought to justice."

The men who pleaded guilty are among 15 who have been charged in the February hijacking of the yacht Quest. Eight others have plea agreement hearings next week.

The yacht owners, Jean and Scott Adam of Marina del Rey, Calif., along with friends Bob Riggle and Phyllis Macay of Seattle, were shot to death several days after being taken hostage several hundred miles south of Oman.

They were the first U.S. citizens killed in a wave of pirate attacks that have plagued the Gulf of Aden and the Indian Ocean in recent years. Prosecutors said the men intended to bring the Americans to Somalia and hold them for ransom there. Court documents made public Friday said they denied a Navy offer to let the Americans go in exchange for taking their boat because they didn't believe they would get the kind of money they were looking for. Ransoms typically pay millions of dollars and this was the second piracy attempt they had made in several days, including a failed attempt to board a container ship. Court records show the men were running out of fuel and couldn't make the return trip to Somalia — about 900 miles away — when they spotted the Americans' yacht sitting in the water and decided to hijack it. At the time, they were aboard a Yemeni boat they had hijacked and persuaded one of their Yemeni hostages to join them on the Americans' boat and share in the ransom money, according to court records.

The Americans were held inside the steering house aboard the yacht the day of the shooting while Mohamud Salad Ali was on board a Navy ship trying to negotiate safe passage to Somalia with the hostages on board, court documents showed.

At some point, Ali Abdi Mohamed fired a bazooka at one of the American war ships shadowing the Quest that was intended as a warning shot, according to court documents. About the same time, he heard gunfire break among the seven men who were guarding the hostages.

Mohamed said he immediately lay down to avoid getting hit and that when he ran through the steering wheel house he found the bodies of the four Americans and several pirates. There were seven men guarding the Americans at the time of the shooting, and four of them died.

Mohamed said in the documents that he charged one of three remaining pirates — Abukar Osman Beyle — and grabbed his weapon in an attempt to immobilize him.

When U.S. special forces scrambled onto the occupied vessel, they found the Americans.

Beyle is among those charged with piracy who does not have a plea agreement hearing. Prosecutors have said additional charges could be forthcoming for several of the men.

"Piracy is big business in Somalia, and today pirates got another reminder of the tremendous cost of participating in this criminal venture. If you pirate an American ship, you will be caught and you'll face severe consequences in an American courtroom," US Attorney Neil MacBride said in a statement.