So much could have gone wrong as SEAL Team Six swept over Pakistan's dark landscape, dropped down ropes into a compound lined by wall after wall, exchanged gunfire and confronted face to face the most dangerous terrorist in the world. The vital things went right.
Just about every contingency the 25 commandos trained for came at them, rapidly, chaotically and dangerously, in their lunge for Osama bin Laden.
They had acted on the best intelligence the US had ever had on bin Laden's whereabouts since he slipped away in the mountains of Tora Bora just under a decade ago. But it was guesswork, too, with the commandos' lives, a president's reputation and a nation's prestige riding on the outcome.
Was the man once seen pacing the compound's courtyard really bin Laden, as it appeared to American eyes? That was just one unknown.
In short, the US had no direct evidence that bin Laden would be there during the assault, or indeed had ever been there. Obama put the raiders in motion on the "pretty good chance" they would find their man, as CIA Director Leon Panetta, who was overseeing the operation back in Washington, put it.
Days after the attack, the administration has fleshed out a reconstruction that is probably more accurate than its initial, flawed telling. More information has been gleaned from the commandos themselves, now back at their home base outside Virginia Beach, Virginia. Some dust has settled.
But there remains no independent or competing account to the administration's story as yet. The reconstruction comes largely from Panetta, White House spokesman Jay Carney and Obama's counterterrorism adviser, John Brennan. Some of their early details proved unreliable.
The only other direct witnesses are the compound's occupants, now in Pakistani custody and, for now, out of reach to anyone else.
Information gaps exist in the official account. Among them: how many armed defenders the raiders encountered, who shot at whom, why none of the compound's survivors was taken away by the Americans, and how many commandos stormed bin Laden's room. It may never be known which commando, or two, killed bin Laden with shots first to his chest, then his head.
The question of exactly what the unarmed bin Laden did to prompt the SEALs to kill rather than capture him has not been settled.
However, officials speaking anonymously told The Associated Press that bin Laden appeared to have been lunging for a weapon in a room that contained his trademark AK-47 assault rifle and side arms. Still, to some in government and intelligence circles, the operation bore the hallmarks of a pure kill mission despite statements from officials that bin Laden would have been taken alive if he had surrendered.
On one point, however, there has been no inconsistency, revision or challenge: The raiders of Team Six made good on their "pretty good chance" and got safely away in a bold mission accomplished.
Late last week, Panetta got the word from the White House that Obama was giving the green light for the raid. Other options, including the idea of "just blowing the place up" from a B-2 bomber, had been discarded, he said. The president's order soon followed.
Obama directed Panetta to proceed under Title 50, meaning this would be a covert operation.
Operational control fell to Adm. William McRaven, head of the Joint Special Operations Command, who is stationed in Afghanistan. Panetta said: "My instructions to Admiral McRaven were, 'Admiral, go in and get bin Laden. And if he's not there, get the hell out."
Team Six was ready.
Its members had rehearsed the assault many times — two or three times a night in Afghanistan, Panetta said. The US had a strong sense for at least several months that bin Laden might be at the compound, which Americans had been monitoring for months longer than that.
Intelligence officials watched so closely that they saw a family's clothes on the third floor balcony and, at one point, a man resembling bin Laden out in the courtyard, Panetta said. They surmised bin Laden and his "hidden family" lived on the second and third floors, because his trusted courier, who had unwittingly drawn the US to this unlikely hideout, occupied the first floor, with his brother in a guesthouse.
When two Black Hawk helicopters carrying the commandos left Bagram Air Base in Afghanistan, stopping in Jalalabad before crossing over into Pakistan on their way to Abbottabad, the operation invited its first risk. Pakistani authorities, kept in the dark about the US mission in their territory, might spot the choppers and engage them.
But the strong Pakistani military presence in Abbottabad, a garrison city with a military academy near the compound, provided a cover of sorts for the Americans. No one would be particularly surprised to hear choppers flying at night.
Reaching their target, the raiders suddenly had to improvise.
Their plan to place a rappelling team on the roof with a second team dropping into the courtyard was jettisoned when one of the helicopters, its blades clawing at hot, too-thin air, had to put down hard. Both choppers landed in the courtyard, behind one ring of walls with more to go.
That was just one of the split-second decisions the SEALs had to make in the lair of al-Qaida's leader.
Gunfire erupted, as the 25 commandos on the ground surely had expected and might even have started.
The compound was also populated with more than two dozen children and women, according to the US The raiders faced life-and-death calls — their own lives and those of the compound's inhabitants — about who was lethal and who was just in their way. That line was not obvious. The SEALs went in with the assumption that some of those they encountered might be wearing explosive suicide vests.
Back at the White House and at a CIA command center, officials including Obama had monitored the operation to this point, apparently on TV monitors although the administration will not say. Special forces are typically outfitted with video.
When the strike force actually entered the compound, Panetta said, 20 or 25 minutes elapsed when "we really didn't know just exactly what was going on."
A violent melee was going on, major details still largely a mystery.
The raiders trying to get into the house breached three or four walls, Panetta said, not specifying whether they scaled them or blew holes.
On the first floor, the SEALs killed the courier and his brother, and the courier's wife died in crossfire. They shot open some doors.
They then swept upstairs and burst into a third floor room, entering one at a time, said Carney. There all the US intelligence, the surmising and the guesswork paid off.
Bin Laden's wife charged at the SEALs, crying her husband's name at one point. They shot her in the calf. Officials told AP that one SEAL grabbed a woman, fearing she might be wearing a suicide vest, and pulled her away from his team. Whether that was bin Laden's wife has not been confirmed.
Also in the room were bin Laden and a son.
The first bullet struck bin Laden in the chest. The second struck above his left eye, blowing away part of his skull.
It is not confirmed whether the shots came from one commando, two or in a spray of gunfire.
The son was shot dead in that room, too.
After the nerve-racking, nearly half-hour gap in information from the scene, Washington got word that "Geronimo" was killed in action.
The raiders' work was not done.
They quickly swept the compound, retrieving possibly crucial records on the operations of Al Qaida.
They destroyed the chopper that gave them trouble. This renewed worries that Pakistani authorities would discover the mission prematurely. Neighbors certainly noticed.
"We had to blow the helicopter," Panetta said, "and that probably woke up a lot of people, including the Pakistanis."
The noncombatants, their hands bound with plastic ties as the operation unfolded, were left for Pakistani officials to round up.
The raiders scrambled aboard the remaining Black Hawk and flew off to the USS Carl Vinson in the North Arabian Sea, bin Laden's body with them. The ground operation had taken about 40 minutes.
Only then was Pakistan informed of what had happened in its land.
Joint Chiefs Chairman Adm. Mike Mullen called Pakistani Army chief Ashfaq Kayani to tell him that an operation he had not known about was complete, a US official told AP. Panetta called his Pakistani counterpart shortly afterward.
Mere hours after the operation, before most of the world knew bin Laden was found and killed, his body was buried at sea.