State Department officials suspected that two Libyan guards hired by its own security contractor were behind an April incident in which a homemade bomb was hurled over the wall of the special mission in Benghazi, according to official emails obtained by Reuters.
But the men, who had been taken into custody the day of the attack, were released after questioning by Libyan officials because of a lack of "hard evidence" that could be used to prosecute them, the State Department emails show.
"Amazing," wrote Eric Nordstrom, then the regional security officer with the U.S. Embassy in Libya, describing the obstacles in prosecuting the suspects.
The April 6 incident involving an improvised explosive device (IED) was a troubling precursor to the September 11 attack on two U.S. government compounds in Benghazi, which killed four Americans, including U.S. Ambassador Christopher Stevens.
U.S. authorities initially said last month's attack occurred spontaneously after protests in the region against a film that lampooned the Prophet Mohammad, but now say it was a pre-planned attack by local militants with possible connections to al Qaeda.
Nordstrom testified last week at a congressional hearing that a string of security concerns before September led officials on the ground in Libya to repeatedly ask for enhanced security, requests that were denied by officials in Washington.
The April attack illustrated concerns among some U.S. officials in Libya that hiring local residents for embassy guard duties could in itself raise security issues.
The emails identified one of the suspects in that incident as a former employee of Blue Mountain Group who had been fired four days earlier for vandalism, and said the other was still working for the company. Both were unarmed guards who performed routine security tasks, such as screening visitors.
Blue Mountain, based in Carmarthen, Wales, had a State Department contract to handle some routine security duties at the mission in Benghazi. It worked in concert with a local partner to screen and hire guards for the U.S. compound in the eastern Libyan city.
The State Department had no immediate comment on the emails, which were obtained by Reuters from a government source. Blue Mountain declined to comment.
Security at the mission has come under congressional scrutiny and become an issue in the U.S. presidential election campaign, with Republicans suggesting the Obama administration failed to adequately protect the mission.
An April 21 email from Nordstrom described difficulties investigating the IED incident, in which no one was injured.
"From the beginning of the investigation there was a big emphasis on the lack of 'hard evidence', and the difficulty in prosecuting anyone," Nordstrom said in his email.
He described how local officials explained that "they did not find an IED on the suspects that they could use to prosecute."
Another email from Antonio Zamudio, acting regional security officer at the Benghazi mission, names three suspects - the former guard fired for vandalism, an active guard who had been demoted from "guard commander to regular guard" and an active guard who owned the vehicle driven that night by the others and was on duty the night of the attack. That third suspect was interrogated and released, the email said.
The first two suspects were taken into custody by the February 17 Brigade, the local militia which acted as the Libyan government's protection force for the Benghazi mission.
The Brigade "lacked the most basic of investigative training or skills," and there was no attempt to obtain statements from suspects within the first 16 hours of their arrests. They also were not separated and were allowed to speak to one another, the email said.
The crude explosive used in the April attack was most likely a "Jelatena" which is "readily available in Benghazi and is commonly used for fishing" and sometimes for celebrations, the email said.
"Local security officials or the local populace do not view the use of the Jelatena device as something overly serious," Zamudio said in the email.