Update: 1/1/10: More confirmation here.

As I speculated here, new reports show the suicide bomber who killed 8 CIA agents yesterday at a U.S. intelligence post in Afghanistan, was a person being groomed to be an informant. He had been invited onto the base, and although he had never been there before, he wasn't searched. As to why he was invited on to the base:

An experienced Central Intelligence Agency debriefer came from Kabul for the meeting, suggesting that the purpose was to gain intelligence, the official said.

Among the seven CIA officials killed was the female base chief, a mother of three. While some reports say the attack happened in the gym, others says it happened as he was getting out of a car. Maybe she walked up to the car to greet the would-be informant and he blew himself up as he was getting out.

The Taliban, which has taken credit for the attack, says the bomber was posing as an Afghan officer. So the CIA thought they had flipped the guy, but he was playing them. This story is still developing.