A federal judge has denied a request from a Somali man accused of piracy to have $1,600 in cash returned to him for humanitarian needs, saying he failed to prove he was lawfully in possession of the money.

Mohammad Saaili Shibin is accused of acting as the chief negotiator for a band of pirates that killed four Americans aboard the yacht Quest.

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 U.S. citizens killed in a wave of pirate attacks that have plagued the Gulf of Aden and the Indian Ocean in recent years, despite an international flotilla of warships that patrol the area. Four U.S. warships were shadowing the Quest and negotiations were underway when shots aboard the sailing vessel were fired.

Ten Somali men have already pleaded guilty for their roles in the hijacking of the yacht and a Yemeni man also has a plea hearing scheduled for Thursday. Prosecutors don't believe any of those men fired the shots that killed the Americans. Three others are also facing charges.

Unlike the other men charged in connection with the case, Shibin never set foot aboard the Quest. Court documents say he researched the Americans online to determine how much of a ransom to seek for them.