The role of the Red Team was to see if there were alternative explanations that could explain the "pattern of life" of the mysterious residents of the Abbottabad compound. For instance: Could they be the retinue of some drug lord who was keeping a low profile? Or might they be on the fringes of al Qaeda but unrelated to bin Laden himself?

On Thursday, April 28, 2011, during the final National Security Council meeting to discuss what to do in Abbottabad, the Red Team briefed the president and his top advisers.

One of the Red Team analysts put the odds that bin Laden was living in Abbottabad at 40%, which was discomfiting to some.

Brennan recalls: "Some of us thought, 'Whoa! We thought the prospects were higher that he was in there.' And the president recognized that when people were saying, 'Well, there's only 40% of a chance,' that some people were going to get a little bit soft on this."

Was it too risky?

The uncertainty that bin Laden was even living in Abbottabad contributed to the advice that Biden and Gates gave Obama during this final National Security Council meeting: Don't authorize the SEAL team raid. It's just too risky.

By now, Brennan had come to a very different conclusion.

He had already told the president privately the CIA officials who had developed the intelligence on Abbottabad were "the people that have been following bin Laden for 15 years. This has been their life's work, this has been their life's journey, and they feel it very much in their gut that bin Laden is at that compound. I feel pretty good, if not certain, that bin Laden is at that compound."

Brennan urged a go on the raid.

As the SEAL raid unfolded in Abbottabad on May 1, 2011, Brennan was as anxious as anyone else in the White House Situation Room: "Might there be a quick reaction force that bin Laden may have had, security that we didn't know about?" he recalled thinking.

The raid, of course, succeeded.

When photos of the dead Osama bin Laden were passed around the Situation Room, Brennan nodded and said, "It's bin Laden."

Follow us on Twitter @CNNOpinion.

Join us on Facebook/CNNOpinion.