LOS ANGELES — After 11 days of interviews, Oscar-winning filmmaker Errol Morris felt he was hardly closer to understanding Donald Rumsfeld than when he first began to work on the documentary “The Unknown Known.”

The film, which gets its title from the former U.S. defense secretary’s famous answer about “known knowns” and “known unknowns” to a reporter’s straightforward question, offers the architect of the 2003 Iraq war and its troubled occupation the platform to explain his worldview and rationale.

“I thought this would be a way in, a way of investigating that question of how we ended up in the place we did,” Morris said in an interview ahead of the film’s release in U.S. theaters on Friday after its premiere at the Telluride Film Festival in Colorado in August.

But Morris, best known for documentaries “The Thin Blue Line” and “The Fog of War,” said he found that when given the chance, Rumsfeld was able to do little more than articulating shallow maxims and self-fulfilling generalizations, what Morris termed “principles you might find in a Chinese fortune cookie.”

“Absence of evidence is not an evidence of absence,” the 81-year-old, who served as secretary of defense for Republican Presidents Gerald Ford and George W. Bush, repeats in the documentary.

“Some things work out, some things don’t. … If that’s a lesson, yes, it’s a lesson,” is another statement that Morris cannot quite get Rumsfeld himself to pin down.

“What really fascinates me is that people were taken in by all of this — this sea of words,” Morris said about the Rumsfeld, who was known to enjoy speaking with the media at length and pontificating about his ideas.

“I don’t know if he sees himself clearly at all,” he added.

“The Unknown Known” is a sequel of sorts to Morris’s Oscar-winning 2003 film “The Fog of War.” In that film, Vietnam War-era Defense Secretary Robert McNamara explains his philosophies on warfare.

But “The Fog of War” gathers its strength from McNamara’s palpable regret at failing and the war’s human cost.

“Many people feel that both Vietnam and Iraq were terrible disasters, not just for the number of people killed on the ground, American soldiers, insurgents, civilians and on and on and on,” Morris said. “But because it really changed our idea about ourselves, about who we are.”

Thousands of memos

Rumsfeld’s thousands of memos over the course of his government career, which began in the Nixon administration, form the core of the film. Pentagon staffers dubbed the memos “snowflakes” as they piled up on desks.

Morris said what fascinated him about the memos was how it gave a first-person narrative to history.

“It’s trying to discover what it is that makes him think: Who is he? Why did he make the decisions that he did? To me there was a great mystery going into it,” he said.

Morris described the memos as a paper trail Rumsfeld could control, unlike the White House audio recordings of his former boss, President Richard Nixon, which are a historical testament to the hubris that brought his downfall.

Rumsfeld supplied declassified memos to Morris in preparation for the film. The director said he probably read more than 1,000 memos, well short of the tens of thousands he estimates were written.

“He revised them and revised them again,” Morris said. “They’re in many ways a record not of the truth, but of how Donald Rumsfeld wanted to be perceived by history or perceived by the people around him.”

Yet the memos only tell a portion of the history, and some critics have raised the point that Morris fails to corner Rumsfeld on torture during the occupation of Iraq and the weapons of mass destruction that were used a pretext for war but ultimately never turned up.

“What I’ve come away with is Rumsfeld’s extraordinary ability to avoid answering questions, to obfuscate, to misdirect, and what was most disturbing … was I felt that he was not just obfuscating, evading for others but also for himself,” Morris said. “I began to wonder: Is this really a person who’s in touch with reality?”

In the end, he cautioned: “I would encourage people to see this movie as a mystery.”