Former Navy SEAL Glen Doherty one of 4 Americans killed in attack on U.S. consulate in Libya

Glen Doherty
CBS Boston/Family photo

(CBS/AP) BOSTON - A former Navy SEAL from a Boston suburb was one of four Americans who died in the attack on the U.S. consulate in Libya Wednesday.

Forty-two-year-old Glen Doherty was killed with U.S. Ambassador Christopher Stevens in Benghazi, a family friend told CBS Boston on Thursday.

"He was on security detail and he was protecting the ambassador and also helping the wounded"' when he was killed, his sister, Katie Quigly told the Boston Globe.

Doherty was a 1988 graduate of Winchester High School.

A third victim has been identified as Foreign Service Officer Sean Smith, an Air Force veteran who had worked as an information management officer for 10 years in posts such as Brussels, Baghdad and Pretoria.

The identity of the fourth American killed is still not known.

A closer look at U.S. ambassador Christopher Stevens
New questions about makers of anti-Muslim film
Romney's Libya gibes aimed to show contrasts with Obama

The four Americans were killed when a group of U.S. employees went to the consulate to try to evacuate staff as the building came under attack by a mob wielding guns and rocket propelled grenades. Stevens is the first U.S. ambassador to be killed in an attack since 1979, when Ambassador Adolph Dubs was killed in Afghanistan.

On Thursday, a senior Libyan security official said the attack was an organized two-part operation by heavily armed militants that included a precisely timed raid on a supposedly secret safe house just as Libyan and U.S. security forces were arriving to rescue evacuated consulate staff. Wanis al-Sharef, eastern Libya's deputy interior minister, said Stevens and another American were killed in the consulate as plainclothes Libyan security were evacuating them to the safe house. The second assault targeted the safe house, killing two Americans and wounding nearly about 30 Libyans and Americans.

Meanwhile the Obama administration has begun what appears to be a terrorist hunt in Libya, as evidence mounts that the attack was perpetrated by well-armed thugs and not an out-of-control crowd.

CBS News correspondent David Martin reports the FBI has opened an investigation into the deaths, and agents will be sent to sift through the wreckage for evidence. They will be accompanied by a second team sent just for their protection.

As part of the hunt for the attackers, officials say the U.S. will increase its surveillance over Libya, including the use of unmanned drones. In addition, the U.S. Navy is positioning two destroyers armed with cruise missiles off the coast of Libya.

One destroyer, the USS Laboon, moved to a position off the coast Wednesday, and the USS McFaul is en route and should be stationed off the coast within days. Officials said the ships, which carry Tomahawk cruise missiles, do not have a specific mission. But they give commanders flexibility to respond to any mission ordered by the president.

The investigation will focus on whether the assault on the U.S. Consulate in Libya was a planned terrorist strike to mark the anniversary of the Sept. 11, 2001, attacks and not a spontaneous mob enraged over an anti-Islam YouTube video.

After the attack, an elite anti-terrorist unit of about 40 Marines was flown in to beef up security at the American embassy in the capital of Tripoli. Air Force transport planes flew the bodies of the dead Americans out, along with at least three who were injured and the rest of the approximately 25 diplomats assigned to the consulate. At the same time, the U.S. State Department urged all non-essential personnel to leave on commercial flights.

Three Americans injured in the assault on the consulate in Benghazi were being treated Thursday at the U.S. military hospital in Landstuhl, Germany, near America's Ramstein Air Base, CBS News has learned.

Wanis al-Sharef, a Libyan Interior Ministry official in Benghazi, said there had been threats that Islamic militants might try to take revenge for the death of al Qaeda's No. 2 commander Abu Yahya al-Libi, who was killed in a U.S. drone strike in Pakistan in June, and he said the U.S. consulate should have been better protected.

Confirming al-Libi's death for the first time in a video posted online Monday, al Qaeda chief Ayman Al-Zawahri called on Muslims in al-Libi's native Libya to take revenge for his death.

U.S. officials believe the militants were using the demonstration against the video as a cover to get into the consulate and then take as much revenge as they could on Americans, Martin reports.

While the White House has been hesitant to call the attack planned, House Intelligence Committee Chairman Mike Rogers was not so ambiguous.

"Absolutely it's a terrorist attack," Rogers told CBS News Capitol Hill producer Jill Jackson. "This was not done by the Libyan government. It was done by an external group we believe has at least extremist ties, maybe al Qaeda ties, and the style and the signature of the attack clearly would be something that we have seen before and would be in line with something al Qaeda would do."

Romney doubles down on WH criticism of attacks
Obama on Libya attack: "Justice will be done"
Libya doctor: U.S. ambassador died of asphyxia

The White House says President Obama called the presidents of Libya and Egypt Tuesday and urged them to continue working with the United States to ensure the safety of diplomatic personnel.

Mr. Obama thanked Libyan President Mohamed Magariaf for his condolences over the deaths of Stevens and the three other State Department officers. The White House says the two leaders agreed to work together to bring the attackers to justice.

During a second call, Egyptian President Mohammed Morsi promised Egypt "would honor its obligation to ensure the safety of American personnel," the White House said.

Mr. Obama told Morsi that while "he rejects efforts to denigrate Islam ... there is never any justification for violence against innocents."