They say that only small groups of Qaeda members remain in the country.
The official declined to identify other Qaeda members thought to have been at the scene.
Four Qaeda members were convicted in 2001 for the embassy attacks.
So far, however, not a single member of Al Qaeda has been discovered.
In at least one of those cases, they said, the techniques prompted an important Qaeda member to give up vital information.
"If he is a member of Al Qaeda, why didn't they keep him there?"
Four members of Al Qaeda are believed to have been killed in the strike.
Some have said there is evidence that the fighters include members of Al Qaeda.
Yet among those who have also called the city home are high-ranking members of Al Qaeda.
Investigators have said he admitted to meeting with members of Al Qaeda several years ago.