The Islamist extremist some are now calling the most dangerous man in the world had a few parting words to his captors as he was released from the biggest U.S. detention camp in Iraq in 2009.

“He said, ‘I’ll see you guys in New York,’” recalls Army Col. Kenneth King, then the commanding officer of Camp Bucca.

King didn’t take these words from Abu Bakr al-Baghdadi as a threat. Al-Baghdadi knew that many of his captors were from New York, reservists with the 306 Military Police Battalion, a unit based on Long Island that includes numerous numerous members of the NYPD and the FDNY. The camp itself was named after FDNY Fire Marshal Ronald Bucca, who was killed at the World Trade Center in the Sept. 11, 2001, attacks.

King figured that al-Baghdadi was just saying that he had known all along that it was all essentially a joke, that he had only to wait and he would be freed to go back to what he had been doing.

“Like, ‘This is no big thing, I’ll see you on the block,’” King says.

King had not imagined that in less that five years he would be seeing news reports that al-Baghdadi was the leader of ISIS, the ultra-extremist army that was sweeping through Iraq toward Baghdad.

“I’m not surprised that it was someone who spent time in Bucca but I’m a little surprised it was him,” King says. “He was a bad dude, but he wasn’t the worst of the worst.”

King allows that along with being surprised he was frustrated on a very personal level.

“We spent how many missions and how many soldiers were put at risk when we caught this guy and we just released him,” King says.

During the four years that al-Baghdadi was in custody, there had been no way for the Americans to predict what a danger he would become. Al-Baghdadi hadn’t even been assigned to Compound 14, which was reserved for the most virulently extremist Sunnis.

“The worst of the worst were kept in one area,” King says. “I don’t recall him being in that group.”

Al-Baghdadi was also apparently not one of the extremists who presided over Sharia courts that sought to enforce fundamentalist Islamic law among their fellow prisoners. One extremist made himself known after the guards put TV sets outside the 16-foot chain-link fence that surrounded each compound. An American officer saw a big crowd form in front of one, but came back a short time later to see not a soul.

“Some guy came up and shooed them all away because TV was Western,” recalls the officer, who asked not to be named. “So we identified who that guy was, put a report in his file, kept him under observation for other behaviors.”

The officer says the guards kept constant watch for clues among the prisoners for coalescing groups and ascending leaders.

“You can tell when somebody is eliciting leadership skills, flag him, watch him further, how much leadership they’re excerpting and with whom,” the other officer says. “You have to constantly stay after it because it constantly changes, sometimes day by day.”

The guards would seek to disrupt the courts along with and any nascent organizations and hierarchies by moving inmates to different compounds, though keeping the Sunnis and the Shiites separate.

“The Bloods with the Bloods and the Crips with the Crips, that kind of thing,” King says.

The guards would then move the prisoners again and again. That would also keep the prisoners from spotting any possible weaknesses in security.

“The detainees have nothing but time,” King says. “They’re looking at patterns, they’re looking at routines, they’re looking for opportunities.”

As al-Baghdadi and the 26,000 other prisoners were learning the need for patience in studying the enemy, the guards would be constantly searching for homemade weapons fashioned from what the prisoners dug up, the camp having been built on a former junkyard.

“People think of a detainee operation, they think it’s a sleepy Hogan ’ s Heroes-type camp,” the other officer says. “And it’s nothing of the sort.”

Meanwhile, al-Baghdadi’s four years at Camp Bucca would have been a perpetual lesson in the importance of avoiding notice.

“A lot of times, the really bad guys tended to operate behind the scenes because they wanted to be invisible,” the other officer says.

King seemed confident that he and his guards with their New York street sense would have known if al-Baghdadi had in fact been prominent among the super-bad guys when he was at Camp Bucca.

King had every reason to think he had seen the last of al-Baghdadi in the late summer of 2009, when this seemingly unremarkable prisoner departed with a group of others on one of the C-17 cargo-plane flights that ferried them to a smaller facility near Baghdad. Camp Bucca closed not along afterward.

Al-Baghdadi clearly remembered some of the lessons of his time there. He has made no videos, unlike Osama bin Laden and many of the other extremist leaders. The news reports might not have had a photo of him at all were it not for the one taken by the Americans when he was first captured in 2005.

That is the face that King was so surprised to see this week as the man who had become the absolute worst of the worst, so bad that even al Qaeda had disowned him. The whole world was stunned as al-Baghdadi now told his enemies “I’ll see you in Baghdad.”