(CBS News) A radical Islamic group called Ansar al Sharia is, according to U.S. officials, the leading suspect in the attack on the U.S. Consulate in Benghazi that killed four Americans. The name means "Supporters of Islamic law" and U.S. officials describe it as an offshoot of al Qaeda.
At least one of the attackers was photographed at the scene, and Libyan officials claim to have already made arrests.
Attorney General Eric Holder cut short an overseas trip to return to Washington and a law enforcement source said the FBI would begin the investigation by interviewing the 30 American survivors of the attack who are now at a U.S. military base in Germany.
The attackers struck at 10 p.m. local time Tuesday, and within 15 minutes were inside the compound firing on the main building, where Ambassador Chris Stevens, Information Manager Sean Smith, and a security officer had already begun destroying classified documents.
Smoke and flames from a rocket propelled grenade which exploded on the roof drove the security officer out of the building, but he went back in to find Stevens and Smith.
State Department Spokeswoman Victoria Nuland described what happened next.
"When he got to Sean Smith he was already dead. He pulled him from the building. He went back into the building with additional security forces but was unable to locate Ambassador Stevens before the fire overcame the building," Nuland said.
The battle then shifted to an annex where two other Americans, former Navy SEALs Glen Doherty and Tyrone Woods were killed, apparently outnumbered and outgunned by their attackers.
The bodies of the four Americans are scheduled to come home Thursday -- a chilling reminder that while Osama bin Laden may be dead his sympathizers are alive and dangerous.
The 30 Americans at the consulate who survived the attack did so by taking shelter in an annex of the consulate. They were hunkered down there for about four and a half hours until Libyan forces finally got control of the situation.
Then the Americans were taken to the Benghazi airport, flown to Tripoli, and from there to Germany.