A federal grand jury in Norfolk indicted Wednesday a Somali man for his alleged role in negotiating the ransom of four U.S. citizens who were held as hostages and later killed by pirates aboard their yacht off the Oman coast in the Arabian Sea.

Mohammad Saaili Shibin, 50, was apprehended in Somalia and transferred to the U.S. He was among 13 Somali men and a Yemeni man who were indicted in March for their alleged role in pirating a yacht, taking four U.S. citizens hostage and killing them before they could be rescued by U.S. officials.

Shibin was not among the conspirators who allegedly sailed and boarded the yacht. But he is accused of being responsible for negotiating with the hostages’ families for ransom.

According to the indictment, Shibin conducted research when the pirates were aboard the yacht for four days in February to learn about the hostages. He triedy to figure out how much ransom to demand and how to contact the hostages’ family members.

While the U.S. military was trying to conduct negotiations with the pirates, they allegedly fired a rocket-propelled grenade at the USS Sterett.

Neil H. MacBride, U.S. Attorney for the Eastern District of Virginia, called Shibin’s arrest a “significant breakthrough in the United States’ battle against Somali pirates.” He called Shibin a “hostage negotiator who operated in Somalia” and said this was the first time the U.S. government has “captured and charged an alleged pirate in a leadership role.”

“We hope that this indictment will strike at the heart of the piracy business and send a strong message to all pirates that they are not beyond the reach of the FBI, whether they board the ships or remain on-shore in Somalia,” MacBride said in a statement.

Shibin and his conspirators are charged with piracy, which carries a mandatory penalty of life in prison. They are also charged with conspiracy to commit kidnapping and the use of a destructive device during a crime of violence.

The Americans killed were Phyllis Macay and Robert A. Riggle of Seattle and Jean and Scott Adam of Marina del Rey, Calif. The four had made their home aboard a 58-foot yacht since December 2004.

When their yacht was hijacked, they were headed to Salalah in the small Arab kingdom of Oman.