The FBI's decision to seize two pirate chiefs amid hostage negotiations off the coast of Somalia on Monday has reportedly come under question days after four Americans vacationing on their 58-foot yacht were killed.

The New York Times reports that an FBI hostage-rescue negotiator aboard the U.S.S. Sterett came to believe the two Somalis were not serious when they boarded the vessel. Once those men were taken into custody, U.S. officials told the pirates on the yacht -- called the Quest -- to send over someone they could negotiate with.

The events that immediately followed have been sharply contested and raises questions about the decision to detain the pirate leaders, the Times reports.

American officials said the pirates on the yacht seemed relieved — even “exceptionally calm” — when they were told their senior commander was cooling his heels in a Navy brig.

Hours later, however, panic ensued among the younger pirates, with some Americans theorizing that a fight had erupted among them, the Times reports.

One person who has talked to associates of the pirates said their leader had told them that if he did not return, they should kill the hostages, though American officials say they do not know that to be the case, the Times reports.

The FBI is investigating the killings of Phyllis Macay and Bob Riggle of Seattle, Washington, and Jean and Scott Adam of Marina del Rey, near Los Angeles, who had made their home aboard the 58-foot yacht since December 2004.

The FBI agent involved was a hostage negotiator from a special team based at Quantico, Va., who was experienced in both domestic and international hostage crises, a law enforcement official told the Times Wednesday. It was unclear whether the agent had ever previously negotiated with Somali pirates.

Click here for more on this story from the New York Times.