When Osama bin Laden was killed by US special forces two years ago, Kathryn Bigelow was deep in preparations for a movie about the failure to capture him during the early stages of the war in Afghanistan. The script, by Mark Boal, was more or less finished; they had scouted locations in Kazakhstan and were preparing to helicopter into Bagram and Jalalabad to see for themselves the terrain they'd be trying to replicate. When news of the death came in, it blew apart the project in such a way, Bigelow says, that any frustration was eclipsed by a sense of being "propelled by history." In fact, she says, "I think our first thought was, 'Well, at least we have a third act.'" As it turned out, Bigelow and Boal, who had successfully collaborated on The Hurt Locker three years earlier, quickly realised it was not a third act but "the entire story." Zero Dark Thirty, which has been igniting feverish reactions since before its first screening, is an account of the 10-year CIA search for Bin Laden and the culminating raid on his compound in Pakistan. It opens with a black screen, over which real audio from 9/11 plays, the screams and entreaties as shocking now as they ever were, and what follows, including scenes of brutal "enhanced interrogation" of detainees in CIA blackspots, is either "a wrenchingly sad, soul-shaking story about revenge and its moral costs" (the New York Times) or "false advertising for waterboarding" (the New Yorker) - a film that, ultimately, "endorses torture." Bigelow only finished the edit two weeks ago and, in a Park Avenue hotel suite in the throes of publicity, has the air of someone surfacing to scenes of unexpected confusion. By Hollywood standards, it was a lightning-quick turnaround - just three months of filming, with India and Jordan standing in for Pakistan and Afghanistan. At 61, Bigelow is a striking figure, slight, angular and tall (5ft 11in). She is softly spoken and pulls awkwardly at the sleeves of her jumper. Her assiduously neutral position on the politics of the film brings to mind, ironically, a politician. There will be many accounts of the war on terror, she says, of which the new film will be just one: a specific story, told from a specific point of view, informed by Boal's interviews with CIA operatives. "I feel very confident with his reporting," she says, "very confident with my handling of his reporting. And I think we can both, with confidence, stand by that film from beginning to end. Not even its harshest critics dispute that Zero Dark Thirty is a beautifully made film, with clean, sharp lines, completely gripping, and light on any extraneous material. There is almost no backstory for the characters, just the grinding sense of mission that propels people working in extraordinary circumstances. There is nothing glorifying about the torture scenes, either, which illustrate both the hideous reality behind the euphemistic language and the fact that you can't trust information coming out of them: when asked for details of an imminent attack, the detainee - beaten, waterboarded, dragged on a leash and finally shut in a box - mumbles in terror and bewilderment every day of the week. Later, when not under duress, he gives up a key name, which critics of the film say sets up a false causality: there is no conclusive evidence that torture led to this particular disclosure. Bigelow's approach to the film and the ensuing furore has clearly been influenced by her experiences on The Hurt Locker. In that movie, the wider controversies of the war in Iraq are sidelined in favour of the experiences of the soldiers: the beads of sweat, the dust, the fly dancing on an eyelash as it looks, unblinkingly, down the barrel of a gun. These small details accrete, over the course of the film, into something like a moral force. Bigelow justifiably won the 2010 Oscar for best director, the first woman to win in that category. Zero Dark Thirty takes "a similar perspective," she says, with its focus on the individuals, a group of CIA agents tasked with finding Bin Laden and played with brilliant understatement by Jessica Chastain, Jennifer Ehle and Jason Clarke. "It's a very human piece and it's a story of determination," Bigelow says. We can all, as human beings, identify with believing in something - believing in something so strongly that there is nothing else in your life. Bigelow (in sunglasses) directing Zero Dark Thirty Furthermore, she says, "It's a real tribute to the men and women in the intelligence community who obviously have to, by the nature of their job, work in complete secrecy. It's a nod of respect and great gratitude. The difficulty here is that expressing respect and gratitude to those involved in controversial interrogation techniques is not quite the same as expressing gratitude to those in the relatively neutral field of bomb disposal. When Bigelow says her aim was "to be faithful to the research, to not have an agenda, to hope that people go to see the movie and judge for themselves," she overlooks the film's structural sympathies. There will, I suggest, be people who argue that torture is such a black-and-white issue that to provoke sympathy for those engaged in it is in itself a reprehensible act. That's an interesting point. But I think that you certainly see the human cost. And also, if it had not been part of that history, it would not have been in the movie. You can't have it one way and not the other way. By "human cost," she means both the bloodied, humiliated form of the detainee in the film and the deadened responses of the CIA agents, some of whom were killed in the 2009 suicide bombing of their base in Afghanistan. Bigelow trusted Boal's reporting when he turned in the script, but I wonder if she insisted on knowing his sources - if, when it came to the most controversial scenes, she needed to satisfy herself that they were double-, triple- or quadruple-sourced. Having worked with Mark on The Hurt Locker, I felt like his attention to detail is so acute - and he comes from the world of investigative journalism - that it's sort of like... He described the way we worked together as he cuts the vegetables and I make the soup. Right, so she didn't feel it necessary to, um, meet the farmer who grew the vegetables? There is a short, confused pause. I suppose. That's one way of looking at it. Bigelow's absolute conviction in her own rightness is a habit of mind she has had since childhood. There is no other way to direct, she says: you wouldn't get through the day. She supposes it came from her parents. Her mother, a Stanford graduate, taught English and her father ran a paint factory. They lived in California and took a mildly modish approach to rearing their only child, subscribing, Bigelow says, "to a certain kind of education where I had to make all... This is so crazy, but as a child I had to make all my own decisions." Such as what? If a friend said, 'Can you sleep over?' I'd go to my parents and they'd say, 'Well, it's up to you.' It was always up to me. It created a tremendous sense of independence, which of course my mother regretted when I left home at 17 and went to school... I suppose being confident in a decision-making process is something that helps me a lot in production. You cannot equivocate. After leaving home, she went first to art college in San Francisco and then on to a fine arts programme run by the Whitney Museum of American Art in New York. At that point her only thought was to become a fine artist: it suited the unsociable side of her nature. Bigelow's diffidence is something she acknowledges with wryness and regret. She finds self-promotion irksome, which is why, perhaps, she promotes Boal so strenuously, calling herself the "delivery system" for his content. Bear in mind that for two years in the early 1990s Bigelow was married to James Cameron, which, I imagine, might turn anyone off the charms of self-promotion. "I'm kind of shy by nature," she says. When you meet with an actor, you have to get very specific very quickly, because you've got a scene to shoot. In a work situation, that comes very easily. Any other situation: not at all. She thinks about it for a moment. It's a strange dichotomy. I wish that I could pretend in my life that I was working. I would probably be much more effective. I don't know. She got into film-making by default, after falling in with some video artists, among them Lawrence Weiner, and being inspired to make a short film herself. It was called The Set-Up (1978) and ran along textbook grad-student lines: a 20-minute exposition of "two-men fighting each other as the semioticians Sylvère Lotringer and Marshall Blonsky deconstruct the images in voiceover." It seemed, she says, "like a very good fit. Film wasn't something I searched for; I backed into it. There followed a series of low-budget films, the odd music video - for New Order, in 1987 - and, in 1991, Bigelow's first big hit, Point Break, the surfing blockbuster starring Keanu Reaves and Patrick Swayze. It established a certain muscularity of style, which Bigelow consolidated with Blue Steel, Strange Days and, in 2002, K-19: The Widowmaker, the Harrison Ford/Liam Neeson nuclear submarine movie that more or less tanked. Navy Seals raid Osama bin Laden's compound in Zero Dark Thirty. Photograph: Jonathan Olley/Columbia Pictures "I can't even think about it," she says on the subject of failure. I feel like there's so much soul-searching going on in the making of a film, it's enough for any given production. I'm content in the knowledge that we've made something we're proud of. That's what gives me the most solace. She is firmly of the belief that commenting excessively on women's restrictions in Hollywood only compounds their ghettoisation - although this is also, surely, another facet of a generally apolitical mindset. "If there's specific resistance to women making movies," she has said, "I just choose to ignore that as an obstacle for two reasons: I can't change my gender, and I refuse to stop making movies." Occasionally, however, there's no avoiding it. The morning of the interview, the novelist Brett Easton Ellis tweets that Bigelow "would be considered a mildly interesting film-maker if she was a man but since she's a very hot woman, she's really overrated." He has since apologised. Was she aware he'd been an arsehole in her general direction? Bigelow laughs. "I was told about it and I just..." She waves a hand dismissively. If not politically, then as a film-maker at least, Bigelow must have been delighted that two of the CIA sources in Boal's script were youngish women. As Lynndie England showed during the Abu Ghraib scandal, women in warfare provoke more complex reactions than their male counterparts. "Well, that's the thing," Bigelow says. Women in defence, I think, are sort of the unsung heroes. I was first of all surprised to learn that women were at the centre of this hunt. And I was sort of surprised that I was surprised. You don't think of a young woman being a terrorist-hunter. Does she think women should be able to serve on the frontline? You know, I don't know. I can't imagine why not. Bigelow has been working on the film with such intensity - "You work in this dark room, you work in this tunnel" - that there has been nothing much outside it for almost a year. Making Zero Dark Thirty was like an epic puzzle, she says, and she sheepishly confesses that's one of the things she likes best: "Logistics - I know it sounds crazy, [but] I do I enjoy it. Because it's like finding order out of chaos. Given the film's scope and ambition, the budget was relatively tight at an estimated $20m. The major expense was recreating the compound where Bin Laden was discovered. Bigelow became obsessed with the accuracy, right down to the fixtures and fittings. We had to build it in a structurally sound way to withstand the rota wash of the helicopters. The production designer even researched what tiles were on the floor, replicated the bed frame and the oak chest of drawers - it was all from the ABC footage they were playing after the assault. When she gives any thought to the vastness of the story, and to the radioactive sensitivity of so many of its elements, she reassures herself that, "as a film-maker, it's a responsibility to engage with the time I live in. You're kind of creating an imagistic version of living history. And with all the risks that entails. Beyond it is blankness. A week or so earlier, when Bigelow left the first screening in New York, Jennifer Ehle walked along the street with her and asked how she was doing. And I said to her, 'I feel kind of... I don't know.' She shrugs and pulls at her jumper. Without purpose all of a sudden. Zero Dark Thirty is released on 25 January.