"In the intelligence community we should encourage, what I would call, good competition," Flynn said. He added: "The DIA, in general, is always going to be a little bit more aggressive. ...As a defense community, we're closer to the war-fighting commanders; it may be in that part of our DNA."
Without the all the varying strands of information pieced together from across the intelligence agencies, officials now say the bin Laden raid would not have happened.
The CIA was running the manhunt, but the National Security Agency was contributing phone numbers and details from conversations it had intercepted in overseas wiretaps. The National Geospatial Agency provided satellite imagery of the Abbottabad compound — from years past and more recently — to get a sense of who might be living there. And it produced photos for a tall man walking the ground inside the compound — even though they were never able to get a close look at his face.
One of the compound's balconies was blocked off by a seven-foot wall, Cardillo said, raising questions about who might want his view obscured by such a tall barrier. Officials also were keeping tabs on the people who lived in the compound, and trying to track how often they went outside.
Cardillo was vocal about his skepticism in each strand of new information he analyzed during the eight months he worked on the case, prompting colleagues to rib him about being a "Debbie Downer."
"I wasn't trying to be negative for the sake of being negative," Cardillo, a deputy national intelligence director who regularly briefs Obama, said in an interview Friday. "I felt, 'Boy, we've got to press hard against each piece of evidence.' Because, let's face it, we wanted bin Laden to be there. And you can get into group-think pretty quick."
To prevent that from happening, officials encouraged wide debate. At one point, they brought in a new four-man team of analysts who had not been briefed on the case to independently determine whether the intelligence gathered was strong enough to indicate bin Laden was there.
Their assessment was even more skeptical than Cardillo's. In the end the call to launch the raid was so close that, as officials have since said, it might as well have come down to a flip of a coin.
In most intelligence cases, the decisions aren't nearly as dramatic. But the stakes are always high.
Over the last four years, the Obama administration has expanded the deadly U.S. drone program in its hunt for extremists in terror havens. The drones have killed thousands of people since 2003 — both suspected terrorists and civilian bystanders — among them four U.S. citizens in Pakistan and Yemen.
The Justice Department this week said only one of the four Americans, Anwar al-Awlaki, who officials believe had ties to at least three attacks planned or carried out on U.S. soil, was targeted in the strikes. The other three were collateral damage in strikes aimed at others.
Though policy officials make the final call on when to strike, the intelligence community builds the case. Analysts must follow specific criteria in drone assessments, including near certainty of the target's whereabouts and the notion that bystanders will not be killed. They must also look at the likelihood of whether the terror suspects can be captured instead of killed.
In these sorts of life-and-death cases, robust debate is especially necessary, Clapper said. And if widespread doubts persist, the strike will be canceled.
"It is a high bar, by the way, and it should be," Clapper said. "If there is doubt and argument and debate — and there always will be as we look at the totality the information we have on a potential target — we damn well better have those debates and resolve those kinds of issues among ourselves the best we can."
Few have been more skeptical of the decision-making behind the drone strikes than Sen. Ron Wyden, an Oregon Democrat who has sat on the Senate Intelligence Committee since 2001. Earlier this year, he threatened to block Senate confirmation of CIA Director John Brennan until the White House gave Congress classified documents outlining its legal justification for targeting American citizens in drone strikes. The documents were turned over within hours of Brennan's confirmation hearing.