KABUL (Reuters) - The two high-ranking U.S. officers were sitting at the nerve centre of one of the most heavily-guarded buildings in Afghanistan when their killer walked into their shared office and shot them both in the head.
The audacity of the attack stunned both NATO and the Afghan government - the gunman had managed to get his weapon through crowded offices and past door after door secured with electronic locks into the heart of Afghanistan's Ministy of Interior.
The killing of Air Force Lieutenant Colonel John D. Loftis, 44, from Kentucky, and another unnamed major, on Saturday also raised awkward questions about the alliance's future strategy in the battle-scarred country.
NATO was hoping military advisors like the two U.S. officers would play a much bigger role in Afghanistan as international troops wound down their involvement in the conflict.
But after the double murder it moved quickly to withdraw all staff from ministries dotted around the Afghan capital.
The two U.S. officers had been working in what workers dubbed "the brain," the two-storey command and control centre located several meters from the main interior ministry building.
With American workers on the ground floor and Afghans above, it buzzes with NATO and U.S. military advisors who coordinate operations with the Afghan National Police.
Their work is a key part of NATO's training mission to create reliable Afghan security forces to take over before foreign combat troops leave by end-2014.
Senior Afghan security sources, who spoke to Reuters on condition of anonymity, say the killer made it past several doors with electronic, push-button locks to reach his targets.
Workers said the men were both well-liked by their Afghan counterparts, who described them as jovial and upbeat.
One of them had even learned Afghanistan's two main languages, Dari and Pashto - a rare feat among U.S. officers in the country - earning him enormous respect.
Colleagues said the men had expressed relief at being away from the front line, in a protected ministry.
"Even though their door had a cypher lock, they would ... open the door to a knock from visitors, that is how safe they felt there," a security source said.
Neither of the men were armed, said sources. Both had removed their body armor before entering the building that is considered the most secure part of the ministry.
Just after 4pm on Saturday, the attacker entered their room, the fourth or fifth office along on the ground floor, and opened fire.
"One of them was shot five times in his forehead, the other got three," an Afghan security source told Reuters.
"After the killer shot them, he casually walked out and closed the door," another source said.
Workers ducked under their desks in panic when the shots rang out. When the bodies were found, some thought the officers had shot each other.
The facts only started to emerge when staff watched CCTV footage and carried out a head count to show one worker was missing.
Authorities have named the chief suspect as Abdul Saboor, 25, a police intelligence officer working at the ministry.
Some have said Saboor, a devout Muslim who knew the Koran by heart, may have been enraged by the burning of copies of the Muslim holy book at a NATO base last week.
Thousands of Afghans have held violent protests over the incident, which NATO described as a tragic blunder. The Taliban later claimed responsibility for the double murder and said the killings were in retaliation for the desecration of the Korans.
Saboor's colleagues said he was very stressed leading up to the day of the shooting, citing family trouble at home, a tiny mountainous village in the Salang district north of Kabul, which has seen little incursion from Taliban forces.
For a day after they attack, a signal from Saboor's mobile phone suggested he might still be in Kabul. But later, the signal shut off and the trail went cold.
Writing by Amie Ferris-Rotman; Editing by Michael Georgy and Andrew Heavens