The US has appealed to armed groups in Libya for help in capturing five people suspected of taking part in last year's deadly attack on its consulate in Benghazi.

The men were identified by the US Federal Bureau of Investigation this week, eight months after the incident that killed four Americans in the eastern Libyan city.

The FBI earlier this month released photos of the suspects captured by security cameras during the September 11, 2012, attack. Among the victims was Christopher Stevens, the US ambassador, who died from smoke inhalation.

The FBI is now trying to locate the men, Al Jazeera reports exclusively.

The US has not officially asked the Libyan government to apprehend the men, but Al Jazeera has learned that US officials have tried to get powerful armed groups to cooperate. So far those groups have been non-committal.

The US knows the Libya government is weak and that the country's official security structures rely on the private brigades for security.

It is not clear what the US administration can do if it does not enlist local support in the investigation.

Acting unilaterally would mean making more enemies.

"They need to give us evidence. Then we can capture them," Adel Belgaid, commander of the Libya Shield brigade, told Al Jazeera.

"But we will carry out our own investigation and they would face trial here. And if US uses ground troops to capture them, this would violate our sovereignty and it will be confronted."

Belgiad, like many people in Benghazi, condemned the death of Stevens. However, there are some that Al Jazeera spoke to who believe Stevens' death was accidental.

"If it was a planned attack, the ambassador would not have died from smoke inhalation," 29-year old Hani said.

"This wasn't the work of al-Qaeda or professional groups because they would have killed him and claimed responsibility."

Belgaid of the Libya Shield said: "There is still confusion as to whether the violence started after the protesters came under fire from inside the consulate."

A Libyan journalist, Feras Busalem, who was outside the embassy compound on the night of the attack, said he saw armed men block the road.

They approached the consulate compound with rocket-propelled grenades and Kalashnikovs and there was a fierce firefight with the embassy guards before they stormed the compound, he said.

Planned attack

The US initially said that the violence was in response to a video posted online that was insulting to Islam. However, recent evidence suggests it was a planned attack.

Discussing the new development, David Mack, a former US ambassador to Libya, said Libya is facing a situation of turmoil in which various groups are contesting for power.

"The government faces some serious constraints in maintaining order," he said.

"We want to help that but we must insist that the perpetrators of this crime be brought to justice."

Mack said it was premature to talk about the US going into Libya unilaterally.

He said the important task right now was to reassert the Libyan presence in terms of security and it was up to the Libyans to decide whether their justice system was capable of dealing with the suspects.

The US no longer has an official presence in Benghazi. But recently, a confirmation hearing of Stevens' successor, Deborah Jones, was held in front of the Senate Foreign Relations Committee.

The appointment has yet to be endorsed by the full Senate.