FBI agents are investigating the Somali pirates who hijacked a US ship and are holding its captain hostage, US officials said Saturday, raising the possibility of federal charges against the men if they are captured. Even as Navy warships were in a standoff with the pirates floating in a lifeboat in the Indian Ocean, FBI agents from New York were investigating how the hijacking unfolded, according to two officials who spoke on condition of anonymity because they were not authorized to discuss the case. "If there were ever a US victim of one of these attacks or a US shipping line that were a victim, our Justice Department has said that it would favorably consider prosecuting such apprehended pirates," Stephen Mull, the acting undersecretary of state for international security and arms control, told Congress last month. Somali pirates boarded and briefly took control of a US cargo ship. The crew thwarted the hijackers, however, and the pirates fled to a lifeboat with Capt. Richard Phillips as hostage.