updated 10/4/2011 11:32:46 AM ET 2011-10-04T15:32:46

A U.S. judge on Tuesday ordered a Somali pirate leader to spend life in prison for his role in the hijacking of a yacht that left all four Americans on board dead.

Mohamud Salad Ali is the fifth of 11 men who have pleaded guilty to piracy in the case to be sentenced. He received a second life sentence he'll serve concurrently with the other one because he also pleaded guilty to hostage taking resulting in death. Ali recruited men for the expedition and served as a negotiator.

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 in February several days after being taken hostage several hundred miles south of Oman.

They were the first Americans to be killed in a wave of piracy that has plagued the Gulf of Aden and the Indian Ocean in recent years.

Their 58-foot sailing vessel had been boarded by a group of Somali men looking to bring the Americans to Somalia so they could be ransomed. But the pirates' plans fell apart when U.S. Navy warships started shadowing them.

U.S. officials attempted to negotiate with the captors but the situation turned deadly after a rocket-propelled grenade was fired from the Quest at the USS Sterett, a guided-missile destroyer 600 yards away.

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U.S. military personnel responded and after a brief gun battle, took control of the yacht. Two pirates were killed and 13 others were captured.

Military officials discovered all four hostages had been shot and killed by their captors.

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