A Somali man who acknowledged commanding a boat full of pirates pleaded guilty Friday to piracy and hostage taking charges in the hijacking of a yacht that left four Americans dead.

Mohamud Hirs Issa Ali pleaded guilty in federal court as part of an agreement that could result in him serving less than life in prison, the mandatory sentence. He is expected to help prosecutors build their case against the three men suspected of shooting the Americans and a negotiator who was based in Somalia and is considered the highest-ranking pirate the U.S. has ever captured.

Ali is among 14 people from Somalia and 1 from Yemen facing charges related to the February hijacking of the yacht Quest. Eleven of those men have plea agreement hearings scheduled over the course of the next week, including two others on Friday.

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

The owners of the Quest, 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 in February.

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. The pirates are typically motivated by the potential for millions of dollars in ransom money.

Court documents say the pirate group intended to bring the four Americans back to Somalia where Mohammad Saaili Shibin would secure a ransom. That plan fell through when four U.S. Navy warships began shadowing the Quest, and the group sent one of the men on board to negotiate with the Navy.

Issa Ali was among those on board who guarded the Americans and carried an AK-47 on board, records show.

The suspected pirates refused to release the Americans and threatened to kill them if they weren’t allowed to bring them to Somalia.

At some point, a rocket-propelled grenade was fired at an American warship and gunshots were fired aboard the yacht. Ali said he didn’t order anyone to shoot the hostages.

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