Taken at first as a random attack unconnected to the activities of the CIA, the 25 January shooting has now provoked a worldwide search, involving US and Pakistani detective agencies as well as Interpol, that may uncover a planned assault on the nerve- centre of US covert operations.
Virginia police believe that the man, who sprayed bullets from an automatic rifle into cars arriving at CIA headquarters in the morning rush-hour, is a 28-year-old Pakistani, Amail Kansi. Mr Kansi, charged in absentia with murder, flew from Washington to Pakistan the day after the incident, before he had been identified as the prime suspect.
Mr Kansi spent a week in Quetta, Baluchistan, where his family has a hotel and orchard business, before vanishing on 7 February, possibly after being tipped off that he was on America's Top Ten Most Wanted list.
Sources in Washington said two senior FBI agents left for the region yesterday to help find Mr Kansi. The search, led by the Pakistani police with help from the CIA station in Islamabad, has been concentrated in remote areas along Pakistan's borders with Iran and Afghanistan.
Virginia police identified Mr Kansi after being tipped off by his former room-mate, also a Pakistani immigrant. In their shared apartment, police found what they believe is the rifle used in the shooting and hundreds of rounds of ammunition along with other weapons. They also matched fingerprints found on one of the spent shells at the crime scene with those of Mr Kansi.
Still puzzling investigators is what motive Mr Kansi may have had for targeting the CIA employees. One theory is that Mr Kansi, who came to the US in 1991, may have been under orders from an Islamic group based in Iran - an idea that would be reinforced if he is found to have fled into Iran.
Also under consideration is the fact that his native area around Quetta served as a base for CIA covert aid to Afghan guerrillas fighting to end the Soviet occupation - activities in which Mr Kansi may have been involved. It could be that Mr Kansi felt at some time let down or slighted by the CIA and was seeking revenge.
The CIA says it has no proof of any links with Mr Kansi. 'We are not aware of any connection, direct or indirect, between Kansi and the CIA,' an agency source said. Until the shooting, however, Mr Kansi worked for a courier agency owned by the son of Chris Marchetti, an aide to Richard Helms, a former CIA director.