Washington (CNN) -- The suicide bomber who killed seven CIA officers and contractors and a Jordanian intelligence official in Afghanistan was within seconds of being searched by two security contractors when he detonated his explosives, a former intelligence official with knowledge of the incident told CNN on Tuesday. On December 30, the two American guards, who worked for Xe Services -- formerly Blackwater USA -- approached the passenger side of the red 4-door sedan where bomber Humam Khalil Abu-Mulal al-Balawi was sitting, the official said. Al-Balawi had been invited to the base to share information he claimed to have that would lead the United States directly to Ayman al-Zawahiri, al Qaeda's second in command.
@highlight
Bomber was invited to base to share information on al Qaeda's second in command
@highlight
He detonated explosives as he left car, former intelligence official says
@highlight
Official: Bomber should've been searched before he got into car; bringing him on base was right
@highlight
Attack shows CIA expansion in Afghanistan, risk to officials, contractors, official says
Xe Services
Blackwater USA
The official observed it was the safest place to be, as "they waited for the @placeholder guys to do what they're paid to do and frisk him."