Story highlights

• Adm. William McRaven says as raid went overtime, he feared Pakistani forces might locate U.S. troops
• He describes how at first the U.S. used a surprising method to verify bin Laden's identity

Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of the new book "United States of Jihad: Investigating America's Homegrown Terrorists."

(CNN)The man who was the architect of the raid that killed Osama bin Laden in the suburbs of a Pakistani city was getting anxious.

He had thought it was possible to keep an element of surprise and evade any response from Pakistan's military if the U.S. Navy SEALs could complete the mission in 30 minutes, Adm. William "Bill" McRaven told CNN last week in his first in-depth interview about the operation.

But after killing bin Laden and his bodyguards, some SEALs went down to the second floor of bin Laden's house and found a treasure trove of hard drives and documents. Now they were trying to pick up all this, which was stretching the time on target.

After about 40 minutes, McRaven was "getting a little bit anxious," he recalled. Speaking to the ground commander, he said, "Hey, get everything you can. But it's time to wrap this up and get out of Abbottabad." As they lifted off from the Abbottabad compound, the SEALs had spent 48 minutes on the ground.

By now the Pakistanis, who he said had no advance knowledge of the operation, had some of their F-16 fighters in the air. McRaven wasn't overly concerned they would be able to engage because they had quite limited ability to fly at night, but he couldn't dismiss the fact that the fighters were now looking for the SEALs' helicopters.

The helicopters had to stop off about midway back from Abbottabad to refuel. They spent 19 minutes on the ground in Pakistan refueling. McRaven said, "That was probably the longest 19 minutes of my life."

A legend in 'Spec Ops'

McRaven is a legend in the special operations community. In 1995 he published "Spec Ops," the standard text on the subject, which grew out of his graduate thesis at the Naval Postgraduate School in Monterey, California. McRaven then worked in the Bush White House -- the first U.S. Navy SEAL to do so -- where he focused on counterterrorism policy. McRaven later rose to become the head of U.S. Special Operations Command, which oversees more than 60,000 people working in special operations and special forces.

Obama: 2011 raid was best shot at bin Laden

McRaven, who retired from running Special Operations Command in 2014 and is now Chancellor of the University of Texas, sat down with CNN to talk about the bin Laden operation.

He first heard the news that the CIA had generated some interesting intelligence about al Qaeda's leader in late 2010 from Adm. Michael Mullen, then the chairman of the Joint Chiefs. McRaven was somewhat skeptical about the new intelligence. After all, there had been a lot of bin Laden "sightings" over the years. McRaven had first deployed to Afghanistan more than half a decade earlier and recalls that there was a bin Laden sighting around every two months, all of which, of course, had to be chased down.

One such sighting had al Qaeda's leader living on top of an Afghan mountain at about 14,000 feet. This sighting, just like so many others, never panned out. That said, Mullen had seen this new bin Laden intelligence and thought it was interesting, so McRaven thought it was certainly worth taking seriously.

Was a raid feasible?

In January 2011, McRaven travelled to CIA headquarters in Langley, Virginia, just outside Washington and was briefed by CIA Deputy Director Michael Morell, who told him about the intelligence that bin Laden possibly might be living in a large compound in the northern Pakistani city of Abbottabad.

McRaven was shown a detailed model of the compound that intelligence officials had created and that was based on overhead imagery of the complex. CIA officials, along with Mullen and Secretary of Defense Robert Gates, wanted to hear McRaven's opinion about the feasibility of a raid on the compound. McRaven recalled that he told the CIA officials, "These are the sorts of things that we in the special operations community have been doing since 9/11. The compounds in Iraq and certainly the compounds in Afghanistan are very similar: high walls, fortified."

McRaven wasn't too concerned about the potential mission from a tactical point of view. What was a real concern was that the compound was in Abbottabad, a city deep inside northern Pakistan.

Over the next several months McRaven went frequently to the CIA for briefings about the mysterious man at the Abbottabad compound who was referred to as "the Pacer" because he would take frequent, quick walks around the compound. These were captured by American satellites, but those satellites could never get a clear view of the man's face.

At this point McRaven could not seek advice about raid options from other SEALs or Delta operators because the "intel" on the possibility that bin Laden was living in Abbottabad was very tightly held. It was so secret that even Gen. David Petraeus, the overall U.S. commander in Afghanistan, was not informed until just before the raid.

McRaven developed something of a cover story for his frequent trips back to Washington. The civil war in Libya was beginning to intensify in the first months of 2011 and options were being considered in Washington that might include the insertion of Special Operations Forces.

Options for the mission

As they contemplated what to do about the possible bin Laden hideout, senior Obama officials considered some courses of action other than a raid. One was to level the compound and any possible subterranean passageways beneath it by dropping some two-dozen 2,000-pound bombs on it. But the compound was in a suburban area and there likely would be significant civilian casualties. Such a large-scale bombing raid also meant that it might never be possible to prove that bin Laden was dead.

McRaven had done considerable research for his book, "Spec Ops: Case Studies in Special Operations Warfare: Theory and Practice," which examined in detail eight successful commando raids since World War II. For the book, McRaven interviewed many of the participants in those raids and also traveled to the locations of the operations. From this, McRaven had developed a theory for special operations, a key component of which was making sure forces arrived at the target before they became vulnerable to detection.

Osama bin Laden: In final days, he was isolated

Informed by this theory, McRaven considered a number of options for the raid. One was to parachute in a SEAL team to a point outside Abbottabad and then have them walk to the target covering some 10 miles on foot.

Another was to drive to Abbottabad, which is some 150 miles from Afghanistan. But both these options had clear points of vulnerability. Whether they traveled on foot or in vehicles, Abbottabad is a city of some 500,000 people and there was too great a risk that the SEAL team would be detected.

Pretty quickly it became apparent to McRaven the only real option was to fly choppers directly to the target from an airbase in Jalalabad, in eastern Afghanistan not far from the Pakistani border.

The helicopter assault had vulnerabilities, too, but they were far less than the parachute drop or long drive options. The main vulnerability was the noise from the choppers' engines and rotors, but McRaven calculated that that noise would not be audible until the helicopters came out from behind a screen of mountains that surrounds Abbottabad. That noise would likely be heard about two minutes flight time from the target. A two-minute window seemed reasonable to McRaven in terms of maintaining the all-important element of surprise.

McRaven's initial plan was not to put the SEAL team in a position where they had to fight their way out of Pakistan. After all, the Pakistanis were a key to the war in Afghanistan because the vast majority of supplies for the some 100,000 American troops then stationed in Afghanistan transited Pakistan by land or across Pakistani airspace.

Five years after Osama bin Laden raid, did it work?

Getting into a firefight with Pakistani soldiers or policemen was something McRaven understood would create serious political problems. The suspected bin Laden compound was only a mile or so from Pakistan's equivalent of West Point and there were also police stations not far from the compound. There was a real risk that Pakistani army and police units might get into a firefight with a strange force that appeared to be invading Abbottabad.

As McRaven kept briefing President Obama and his team, the President made it clear that if it came to a firefight with the Pakistanis he could live with it, telling McRaven, "Look, I want to make sure your troops are safe. If we get bin Laden, that's obviously the mission, but I also want to make sure the troops get back safely." With that clear directive McRaven assembled a "package" of sufficient helicopters and a QRF (quick reaction force) on the other side of the border in Afghanistan so that if it came to a firefight, the SEALs could fight their way out of Pakistan.

In early April, McRaven presented to the President and his senior advisers in the Situation Room a helicopter raid into the compound designed to capture or kill bin Laden. Obama said, "Can you do this?" McRaven replied, "Mr. President, I won't know if we can do this until I have an opportunity to bring in the SEALs and the helicopter pilots from the 160th (Special Operations Air Regiment) and to rehearse it." The President asked, "How much time do you need?" McRaven replied, "Mr. President, I need about three weeks." Obama said, "OK, you have three weeks."

The dress rehearsal

The SEAL team proceeded to hold rehearsals in North Carolina and Nevada involving flying the full 162 miles to the target, refueling the helicopters and practicing on a full scale mock-up of the compound. Mullen and a number of other senior Pentagon and CIA officials went to watch the full dress rehearsal. After three weeks McRaven reported back to Obama and his national security team that the rehearsals had been completed and he was confident the SEALs could do the mission.

Four days before the raid was supposed to launch, McRaven flew to Afghanistan. There he received a call from the President, who asked, "What do you think?" McRaven replied, "Well, Mr. President, if he's there we'll get him. And if he's not, we'll come home."

Osama bin Laden's will, personal letters made public

McRaven said, "Regardless of what your politics are you would have been incredibly proud of how the President and his national security team handled this very, very difficult and ambiguous situation. There was never any discussion about politics and whether or not the decision the President may or may not make, how that would affect his political career. ... Being the junior man in the room and watching this unfold, having been in the military at that point in time, 34 years, I was very proud of the way the President and his team really walked through the details of this mission, asked the hard questions, looked at the options. And then obviously the President, who bore the sole responsibility for the decision, decided to go forward with this even when the intelligence was at best 50/50."

McRaven initially planned to launch the mission on Saturday, April 30, 2011, but there was low-lying fog in some of the valleys that the choppers would be flying through that night. McRaven said, "I didn't wanna rush to failure." He moved the mission to the next night.

A blackout

On the night of Sunday, May 1, there was no moon. Around 10 p.m. in Jalalabad, the SEALs took off in two stealth choppers as well as two backup Chinook helicopters for the 90-minute flight to the Abbottabad area. That night there was no electricity on in Abbottabad. McRaven said, "There are some out there that believe that we were clever enough to turn the electricity off. I can tell you that was not the case. I think there was just a blackout." Blackouts are common in Pakistan.

All was going well with the mission until the lead stealth Black Hawk was approaching the Abbottabad compound. The Black Hawk descended into the compound but abruptly lost "lift" and started to descend very quickly. McRaven saw on a video feed that the chopper was going into a controlled crash. He wasn't overly concerned with what he was seeing. McRaven had lost several helicopters in the course of his time leading Joint Special Operations Command and he knew what a real crash looked like.

Secrets of the bin Laden treasure-trove

McRaven had also spoken to the helicopter pilot ahead of time because he was concerned that when the chopper descended into the compound that a guard might come out of the third floor of the building in which bin Laden was believed to be hiding and fire a rocket propelled grenade, an RPG, or shoot small arms at the helicopter.

McRaven had snipers in the helicopter ready to deal with that eventuality, but the helicopter pilot had also told him, "Look, if I take an RPG or I take small arms, unless I'm killed in the action, I can get that helicopter into what we refer to as the animal pen." The animal pen was the area in the suspected bin Laden compound where cows and chickens were kept.

On the video feed, McRaven could see that the men who were in the downed helicopter had clambered out and were moving on with the mission, which was first to secure one of the smaller buildings on the compound and then proceed into the ground level of the suspected bin Laden living quarters. Along the way they shot and killed both bin Laden's bodyguards, his son Khalid and the wife of one of the bodyguards.

The stairway in the three-story living quarters was barricaded with a steel gate that the SEALs had to blow open. The SEALs then rushed up the stairs of the living quarters toward the third floor. The first SEAL operator coming up the stairs saw a man peeking out through a door on the third floor. The operator later told McRaven, "I knew immediately it was bin Laden." The operator fired at him. Two other SEALs also shot bin Laden inside his bedroom on the third floor.

McRaven heard the ground commander saying, "For God and country, Geronimo, Geronimo, Geronimo." The code word "Geronimo" was ambiguous as to whether bin Laden had been captured or killed. McRaven said it quickly occurred to him, "Well, did we capture him? Or was he killed? Was Geronimo EKIA (enemy killed in action)?" McRaven spoke to the ground commander, who clarified, "Yes. Geronimo EKIA."

McRaven said that while many have speculated this was a straight-kill mission, it wasn't. There was a real fear that bin Laden would, like other leaders of al Qaeda, be wearing a suicide vest, maybe even sleep in a suicide vest, but the rules of engagement for the operators were that if they categorically found that bin Laden was not a threat, his hands were up in the air, and he wasn't wearing a suicide vest, then they had to capture him. If bin Laden had been detained he would have been taken to the massive U.S. base at Bagram not far from Kabul.

McRaven believed that the optimal time to be "on target" was no more than half an hour. By the time the Geronimo code word came through, the operation was 17 to 18 minutes in. McRaven recalled, "I'm watching the clock. And I am watching what is going on around the compound. Of course by this time, we have a helicopter that's down in the compound. The Pakistanis we know are beginning to realize something is happening in Abbottabad. And you can begin to see them trying to figure out what best to do."

'Can you confirm it's bin Laden?'

Around the time the helicopters were landing back in Jalalabad, President Obama asked McRaven, "Bill, can you confirm that it's bin Laden?" McRaven left the video teleconference with the President and walked over to the hangar where the SEALs had offloaded the body. McRaven unzipped the body bag. It was bin Laden. "He didn't look terrific. He had two rounds in his head," McRaven said. The SEALs had several photos of bin Laden. As soon as they put the photos close to the face, it was immediately obvious that it was al Qaeda's leader.

Was there a cover-up in bin Laden killing? (Opinion)

McRaven knew that bin Laden was about 6-foot-4. After removing his remains from the body bag, McRaven saw a young SEAL standing nearby. McRaven asked, "Son, how tall are you?" The SEAL replied, "Well, sir, I'm about 6-foot-2." McRaven said, "Good, come here. I want you to lie down next to the remains here." The young SEAL said "I'm sorry, sir. You want me to do what?"

McRaven replied, "I want you to lie down next to the remains." "OK, sir," said the SEAL. The remains were a couple of inches longer than the young SEAL.

McRaven returned to the videoconference and told Obama, "Mr. President, I can't be certain without DNA that it's bin Laden, but frankly, it's probably about 99% chance that it is bin Laden. In fact, I had a young SEAL lie down next to him, and the remains were a little taller."

There was a pause on the other end of the videoconference. The President came up on the video saying, "Bill, let me get this straight. We have $60 million for a helicopter, and you didn't have $10 for a tape measure?" McRaven said, "It was one of those light moments in the middle of a very anxious time in our nation's history. And it was kinda perfectly timed. It lightened a very tough moment."

A couple of days later, the President presented McRaven with a tape measure mounted on a stand.

Bin Laden was buried at sea. DNA obtained from bin Laden relatives gave a 100% match that it was al Qaeda's leader.

On May 6, four days after the raid, Obama traveled to Fort Campbell, Kentucky, home to the 160th Special Operations Air Regiment. There he met with the SEAL team and the helicopter pilots who had carried out the mission. The President didn't ask who had taken the kill shot and no one volunteered who had done so.

Fighting back tears as he reflected on the many years of sacrifice that had preceded the bin Laden raid, McRaven said, "The President understood everybody was part of this and it wasn't just the SEAL team and the Night Stalkers (helicopter pilots), it was everybody that has fought in the Iraq and the Afghanistan wars after 9/11. ... There may have been one person that pulled the trigger, but there were hundreds of thousands of troops behind us."