An Army carry team moves the flag-draped transfer case holding the remains of Staff Sgt. James Moriarty at Dover Air Force Base on Nov. 7. Moriarty and two other soldiers were killed when their convoy came under fire as it entered a Jordanian military base. (Alex Wong/Getty Images)

Officials investigating the slayings of three U.S. soldiers in Jordan this month say they now know precisely how the Americans were killed but still lack a clear explanation for why a Jordanian guard opened fire on the men as they returned to their base from a training mission.

Surveillance video and witness accounts confirm that the soldiers from the 5th Special Forces Group were shot without provocation as they prepared to enter Prince Faisal Air Base in southern Jordan on Nov. 4. Yet, more than two weeks later, no information has emerged linking the guard to extremist groups or causes, according to U.S. and Middle Eastern officials familiar with the ongoing probe.

The shooter, who was critically wounded in an exchange of fire with the Americans, has remained in an induced coma in a Jordanian hospital since the incident. A team of investigators led by the FBI has conducted an extensive search for possible connections to terrorist groups, interviewing relatives and associates and scouring the man’s computer and cellphone, so far without finding links to jihadists or even evidence of strong religious views, the officials said, speaking on the condition of anonymity to discuss an ongoing investigation.

The absence of such evidence has hampered efforts to determine whether the shooting was an act of jihadist-inspired terrorism or was triggered by a grudge, mental illness or some other cause, said a senior Middle Eastern security official briefed on the preliminary findings.

What appears certain, however, is that the guard fired deliberately and repeatedly at the Americans, shooting one of them as the victim tried to take cover, the official said. “What we don’t know at this point is what exactly set him off,” said the official.

[Slain U.S. soldiers were working for CIA training Syrian soldiers]

The Defense Department and the CIA both declined to comment on the investigation.

The soldiers — Staff Sgt. Matthew Lewellen, Staff Sgt. Kevin McEnroe and Staff Sgt. James Moriarty, all based at Fort Campbell, Ky. — were detailed to a CIA-led training program for Syrian opposition fighters at the time of the incident. All were killed as their convoy was preparing to enter the Jordanian facility near the village of al-Jafr, in what is believed to be the deadliest single incident involving a CIA team since December 2009, when seven officers and contractors were killed in a suicide bombing in Khost, Afghanistan.

Jordanian officials earlier suggested that the shooting might have been triggered by an accidental gun discharge or a failure by the Americans to follow established security protocols for entering the military base, about 150 miles south of Amman, U.S. and Middle Eastern officials said. But evidence from the surveillance video and surviving witnesses has all but ruled out the possibility that a misunderstanding caused the event, the officials said.

A spokesman for the U.S. Embassy in Jordan said in a statement last week that there was “absolutely no credible evidence” that the Americans had violated security procedures at the gate. He added that all possible motives, including terrorism, were still being explored.

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One official familiar with the surveillance video said it shows the convoy’s lead vehicle being cleared through the gate. But as the second vehicle approaches the barrier, bullets are seen to rip through the windshield, hitting the two occupants inside.

Two U.S. soldiers then leap from other vehicles in the convoy to take cover behind a concrete blast wall. But the Jordanian guard, wearing body armor and carrying his assault rifle, is seen in the video to charge toward the Americans, firing several bursts into one of them. The fourth U.S. soldier then fires back at the guard with his pistol, hitting him several times, the official said.

The wounded Jordanian was described by investigators as a seasoned noncommissioned officer and father of three children, with a clean record and extensive experience on the base.

Jim Moriarty, father of slain Staff Sgt. James Moriarty, said he has been briefed on some details of the attack but is still waiting to learn how his son could have been killed at a secure military facility while transiting a gate he and his comrades used regularly.

“They lived on this base, they went through that gate all the time,” Moriarty said in an interview. “I got no rational explanation for what happened other than that this guy killed these Americans on purpose.”

Moriarty said he had been skeptical of the earlier stories about an accidental discharge by one of the Americans’ weapons, noting that the soldiers were highly skilled experts who were in Jordan to train Syrians on the use of firearms. But he added, “I want the truth to come out, whatever the truth is.”

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