A federal grand jury has indicted 13 Somalis and 1 Yemeni “for allegedly pirating a yacht and taking hostage four U.S. citizens, who were ultimately killed before their release could be secured,” federal law enforcement officials say.

The men are expected to appear in a federal court in Norfolk, Va., where the case is being handled. They have been in U.S. custody since they were taken aboard the USS Enterprise last month at the end of a hostage standoff.

U.S. naval forces had been tracking a hijacked American yacht, the Quest, when they heard gunfire on the boat. When a special forces team boarded the Quest, they found that the four captives were dead.

The AP has more:

The boat’s owners, Jean and Scott Adam, along with Bob Riggle and Phyllis Macay, were shot to death after pirates took them hostage several hundred miles south of Oman.

It was the first time U.S. citizens have been killed in a wave of pirate attacks that have plagued the Gulf of Aden and the Indian Ocean in recent years.

Agents from the FBI and the Naval Criminal Investigative Service will announce the indictments in a news conference at 1 p.m. ET Thursday.

Earlier this year, a Somali pirate was sentenced to more than 33 years in prison in a case stemming from the 2009 hijacking of the Maersk Alabama container ship. The Maersk Alabama was back in the news yesterday — for having to fend off yet another attempt to take the ship. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.