Washington (CNN) -- President Barack Obama gave the go-ahead for U.S. forces to raid a northern Pakistan housing compound based on "what was probably a 50-50 chance that Osama bin Laden was there," his national security adviser said.
"It was a circumstantial case ... But what he had 100 percent confidence in was the ability of our special forces to execute the mission," Tom Donilon told CNN's Candy Crowley on Saturday, part of an interview that aired Sunday on "State of the Union."
On April 28, Obama attended the last of several National Security Council meetings focused on finding and going after the al Qaeda leader. During that meeting, some advocated for the commando raid while others advised against it, Donilon said, given there had been no clear-cut sightings of bin Laden by that point.
"He had gotten divided counsel, and that happens a lot in these things, as you would imagine," Donilon said.
After a night's sleep, Obama told Donilon at 8:20 a.m. the next day to draft the order for the raid. By Sunday evening -- which was early Monday morning in Pakistan -- the 38-minute mission was over, the 25-strong U.S. team having flown out of the country along with bin Laden's dead body.
Like other Obama administration officials, Donilon applauded the decision and its end result of knocking out the No. 1 man on the FBI's "Most Wanted Terrorist" list. He called it "the single biggest achievement we've ever had" in the fight against al Qaeda.
Especially as they continue poring through voluminous material taken from the complex, U.S. authorities are more convinced than ever that bin Laden had a significant operational and strategic role, not to mention a key symbolic one, in the terrorist network. His death, said Donilon, is a major blow to al Qaeda.
"At the end of last year, we assessed that al Qaeda had been diminished ... to its weakest since 2001," said the security adviser, who previously served in the administrations of presidents Jimmy Carter and Bill Clinton. "And they took a very big step back Sunday."
One reason for that assessment is what Donilon called the "extraordinary" amount of intelligence that U.S. special forces were able to take from the Abbottabad compound. A multi-agency task force is currently poring through those documents, computer hard drives and other materials -- intermittently releasing information including five videotapes featuring bin Laden that came out Saturday.
"This is the largest cache of information gotten from a senior terrorist -- gotten from any terrorist in one operation," Donilon said, calling the amount of seized material about equal to "the size of a small college library."
Despite doubts from some conspiracy theorists, al Qaeda itself has admitted that bin Laden was killed. That means that his deputy, Egyptian doctor and radical Ayman al-Zawahiri, will rise to the top of the FBI list, according to Donilon, even as U.S. and allied forces continue their efforts to find him and other al Qaeda leaders.
Last week, CIA Director Leon Panetta (who Obama has nominated to succeed Robert Gates as defense secretary) told House members during a closed-door briefing that Pakistan was "either involved or incompetent," according to two sources in attendance. There have been no indications Pakistani authorities knew about or acted upon knowledge that bin Laden was living in the same town as one of its top military academies.
Donilon did not suggest Pakistani authorities knew the al Qaeda leader lived in the city, about 30 miles (50 kilometers) north of the capital Islamabad, or that they somehow harbored him. He said, "I have not seen any evidence, at least to date, that the political, military or intelligence apparatus knew about the presence of Osama bin Laden."
Yet U.S. authorities are troubled by the fact that the al Qaeda leader could stay there "for six years or so" undetected, said Donilon.
"We'll clearly be working with (Pakistani authorities) to understand how we got to this point," he said.
Donilon noted Pakistan's active role in tracking down terrorists, calling them a "very important partner" despite the existence of some "differences" with U.S. authorities. He said, "If we find things ... that are highly disturbing, we'll certainly press that" -- though he expected that Islamabad and Washington would continue to work together.
"We need to look at this in a calm and cool way," Donilon said, adding, "a relationship with Pakistan, given everything we have at stake in that region, is an important relationship."