Documentarian Alex Gibney says he got on board as an exec producer of Hulu’s drama series The Looming Tower because it “seemed like a story that could not be told in pure documentary terms,” but he knew his experience would be a “very useful” tool to “find the reality of the drama.”

The 10-episode straight-to-series adaptation of Lawrence Wright’s Pulitzer-winning 9/11 exposé traces the rising threat of Osama bin Laden and Al-Qaeda and takes a controversial look at how the rivalry between the CIA and FBI set the stage for the attack, and the war in Iraq that followed.

Peter Sarsgaard plays Martin Schmidt, a CIA analyst under orders to share intelligence with John O’Neill (Jeff Daniels) and the FBI, but opts instead to hoard information, believing the CIA is the only agency equipped to battle potential terrorist threats.

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The Looming Tower is based on true events but, in the context of creating the series, some characters are composites and stories are rendered in “dramatic terms,” Gibney explained, by way of distinguishing this from his docu work. “But, in terms of understanding the roles these agencies play and how they tracked Al-Qaeda at the time,” it is essentially the same, he said.

Wright called the book “probably the most important thing I’ll do with my professional life.” He interviewed about 600 people, starting with those who attended O’Neill’s funeral, asking them who else he should interview. “Eventually, you populate the universe of this story.”

“I had to find a way to take this vast tragedy and make it human.” The book started, he said, when he spotted a Washington Post obituary on O’Neill, who died at the World Trade Towers on September 11, 2001. The counter-terrorism expert, who had been the special agent in charge in the FBI, was well versed in the 1993 World Trade Center bombing and assisted in the capture of that plot’s leader, and was considered an expert on Al-Qaeda and bin Laden. After being pushed out of the FBI, he became head of security at the World Trade Center where he died in the collapse of the north tower.

Wright told TV critics when he saw the WaPo report on O’Neill’s death, he was struck that the man who was supposed to “get bin Laden did not get him – bin Laden got him.” Wright told TV critics that one of the people he interviewed reported having told O’Neill he would be safe running security at World Trade Center because al-Qaeda had already tried to bomb it; O’Neill responded ,”They’ll be back to finish the job.”

“He instinctively placed himself at Ground Zero,” Wright said.

Daniels described O’Neill as “belligerent,” someone who “gulped life” and who “blasted people when he did not get his way…but in the end he was right.”

“That was interesting to play and, as I told [writer Dan Futterman] when I signed on, I had no clue how to play it.”

Asked if the agencies are now better prepared, Wright said, “Since 9/11 the intelligence community has been reorganized and is more efficient, but so is Al Qaeda…the threat from terrorism is not diminished.”