BENGHAZI, Libya - The U.S. dispatched an elite group of Marines to Tripoli on Wednesday after the mob attack that killed the U.S. ambassador and three other Americans. Officials were investigating whether the rampage was a backlash to an anti-Islamic video with ties to Coptic Christians or a plot to coincide with the anniversary of 9/11.
Tuesday's stunning attack on the American Consulate in Benghazi poses a daunting task for U.S. and Libyan investigators: searching for the culprits in a city rife with heavy weapons, multiple militias, armed Islamist groups and little police control.
The one-story villa that serves as the consulate was a burned-out wreck after the crowd armed with machine guns and rocket-propelled grenades rampaged through it. Slogans of "God is great" and "Muhammad is God's Prophet" were scrawled across its scorched walls. Libyan civilians strolled freely in charred rooms with furniture and papers strewn everywhere.
A man looks at documents at the U.S. consulate in Benghazi, Libya, after an attack that killed four Americans — including Ambassador Chris Stevens — Wednesday. The graffiti reads, “No God but God,” “God is great” and “Muhammad is the prophet.”
President Barack Obama vowed in a Rose Garden address that the U.S. would "work with the Libyan government to bring to justice" those who killed Ambassador Chris Stevens, information manager Sean Smith and two other Americans who were not identified. Three other Americans were wounded.
Stevens was the first U.S. ambassador killed in the line of duty in 30 years.
"We reject all efforts to denigrate the religious beliefs of others, but there is absolutely no justification for this type of senseless violence. None," said Obama, who also ordered increased security at U.S. diplomatic posts abroad.
Republican Mitt Romney accused the Obama administration of showing weakness in the consulate killings.
The mob attack on Tuesday - the 11th anniversary of the Sept. 11, 2001, terrorist strike in the U.S. - was initially presumed to have been a spontaneous act triggered by outrage over a movie called "Innocence of Muslims" that mocked Islam's Prophet Muhammad that was produced in the U.S. and excerpted on YouTube. The amateurish video also drew protests in Cairo, where angry hardliners climbed the U.S. embassy's walls, tore down an American flag and replaced it with an Islamic banner.
But a U.S. counterterrorism official said the Benghazi violence was "too coordinated or professional" to be spontaneous. The official spoke on condition of anonymity because he was not authorized to discuss the incident publicly.
The FBI was sending evidence teams to Libya, a law enforcement official said.
Libya's new leadership - scrambling to preserve ties with Washington after U.S. help to overthrow former dictator Moammar Gadhafi - vowed to find those behind the attack. Interim President Mohammed el-Megarif apologized to the United States for what he called the "cowardly" assault, which also killed several Libyan security guards at the consulate.
Parliament speaker Omar al-Houmidan suggested the attack might have been planned, saying the mob "may have had foreign loyalties" - an apparent reference to international terrorists. "We are not sure. Everything is possible," he said.
About 50 U.S. Marines were sent to Libya to guard diplomatic facilities. The Marines are members of an elite group known as a Fleet Antiterrorism Security Team, or FAST, whose role is to respond on short notice to terrorism threats and to reinforce security at embassies.
The Marines, sent from a base in Spain, were headed initially to the U.S. Embassy in Tripoli, not to Benghazi, according to U.S. officials, who spoke on the condition of anonymity.
There also were indications that two distinct attacks took place - one on the consulate, then a second hours later early Wednesday on a nearby house to which the staff had been evacuated.
The crowd of several thousand that descended on the consulate was armed with machine guns and rocket-propelled grenades, said Wanis el-Sharef, the deputy interior minister of Libya's eastern region.
A small contingent of Libyan security protecting the facility fired in the air, trying to intimidate the mob. But faced with superior size and firepower, the Libyan security withdrew, el-Sharef said. Gunmen stormed the building, looted its contents and torched it, he said.
Stevens, 52, and a consulate staffer who had stayed behind in the building died in the initial attack, el-Sharef said.
Hours after the storming of the consulate, a separate group of gunmen attacked the other building, opening fire on the more than 30 Americans and Libyans inside. Two more Americans were killed, he said.
Dr. Ziad Abu Zeid, who treated Stevens, said Stevens died of asphyxiation, apparently from smoke.
In a sign of the chaos, Stevens was brought by Libyans to the Benghazi Medical Center with no other Americans, and no one at the facility knew who he was, Abu Zeid said.