Story highlights Ex-Navy SEAL Robert O'Neill says he fired shots that killed Osama bin Laden

O'Neill says he's concerned he'll face prosecution for publicly telling his story

He says value of sharing details with families of 9/11 attack victims makes risk worthwhile

The Navy SEAL who says he shot and killed Osama bin Laden says he is worried the Pentagon might prosecute him for publicly telling his story of the May 2011 raid on the al Qaeda leader's compound in Pakistan.

But Robert O'Neill said the value of sharing the details of the mission for the families of the September 11, 2001, victims and military veterans killed in the ensuing wars makes that risk worthwhile.

"I think I did this in a way that doesn't violate any tactics or any rules," he said in an interview on CNN's "The Lead" with Jake Tapper.

Being prosecuted, he said, "does concern me, and if it comes up, I'll address it."

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In his most extensive live television interview to date, O'Neill said he realized the power of his story while speaking with a group that included about 20 families of victims of the September 11 attacks. He said it was the first time he'd really spoken about the mission, and that men and women cried and told him "it was closure for them."

At that moment, he said, he realized the importance of sharing what he could -- and that he needed to find a way to do so "with respect for the tactics, for the safety of our troops and for the Department of Defense."

Responding to criticisms from former administration officials and current servicemembers that he shouldn't be talking publicly, O'Neill said, "I think it's important historically for this to get out there."

"We were the end of a long, long time of grieving," he said. "We were everybody on that mission. You know, we were the Port Authority, the police department, the NYPD, the FDNY, we were the American people, the 9/11 families, and we were able to go there -- and just that I was able to be a part of that is just the greatest honor that's ever been asked of me."

O'Neill described many of the details of the mission -- and his preparation beforehand.

He said he believed there was "about a 90 percent chance that we weren't going to come back." Among the possible threats: Pakistan's military, unaware of the mission, could shoot the two helicopters down. Bin Laden's house could be wired with explosives. Others in the house could be wearing suicide vests.

"The house getting blown up, possibly getting shot down, suicide bombers, and then possibly running out of gas was a concern," he said. "The chances of us not coming back were a lot greater than the chances we were coming back."

He said he called his family members beforehand -- not offering details on what he was doing, but knowing that they'd soon find out no matter how the mission ended. He also wrote letters to his young children, only to be delivered if he didn't survive at a later date when, for instance, he wasn't there for their weddings.

After the mission started, O'Neill described landing outside bin Laden's compound on the second of two helicopters, after the first one had crash-landed. He said he was the eighth SEAL in line as they moved from the compound's first floor to its second.

On that floor, six ahead of him split off to take out bin Laden's son, clear other rooms and identify potential threats. He was now second in line headed to the third floor, where they expected to find bin Laden.

As the group reached the third floor, he said, the SEAL in front of him dove on top of an "unknown" person -- it turned out to be a woman -- to absorb what they feared could be a blast from a suicide vest. He said he thought "let's get this over with" as he entered the room expecting to be blown up by bin Laden.

That's when O'Neill identified the al Qaeda mastermind.

"I shot him twice in the head, he fell on the floor," he said. "I shot him one more time, and I killed him."

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The magnitude of what he'd done didn't register immediately. O'Neill first worried about eliminating other potential threats -- moving a woman and child out of the way, and then clearing the room.

"It wasn't until the room was cleared and there were more SEALs in the room that it kind of hit me. I had a moment of pause," he said.

A friend put his hand on O'Neill's shoulder.

"I said, 'Hey, what do we do now?'" O'Neill said. "He said, 'Now we go find the computers.' I said, 'OK, I'm back.'"

The 90-minute flight back to the U.S. air base in Afghanistan was stressful, too, as the SEALs counted down the time until they exited Pakistan's airspace.

Then, they could exhale. One SEAL laid next to bin Laden's body to measure his height -- part of confirming his identity. The group hadn't brought a tape measure.

Later, O'Neill sat feet from bin Laden's body, eating a breakfast sandwich and watching a flat-screen television, while watching President Barack Obama announce to the world that the United States had killed bin Laden.

"I think," he told CNN, "I was part of a team full of heroes."