A little-known attempted murder of Richard Nixon is the subject of a new film starring Sean Penn. Donald Clarke talks to first-time director Niels Mueller about handling the most mercurial of movie stars

NIELS Mueller, who looks a little like a less hideous Mick Hucknall, admits to being born during the Kennedy administration and would, therefore, have been alive to world events in the mid-1970s. Nonetheless, when the director came across references to one Samuel Byck while researching presidential assassination attempts - this was for a script, you understand; Niels is not a conspiracy nerd - the name rang no bells.

In 1974, Byck, a deranged tyre salesman, whose already formidable hatred of the establishment had been further stoked by his failure to secure a small-business loan, boarded a plane in Baltimore airport with the intention of forcing the pilot to fly into the White House. After an altercation in which Byck shot two crewmembers - one fatally - the hijacker himself was slain by police officers.

"It was extraordinary," Mueller says. "I was interested in writing a script about a guy who makes an assassination attempt to make the world pay attention, but barely gets noticed. And this was exactly Byck's story."

The assassin's timing could not have been worse. The American public, absorbed by Richard Nixon's pathetic attempts to shrug off any responsibility for the Watergate cover-up, barely registered events in Baltimore. Not only did Byck fail to become a Lee Harvey Oswald, he didn't even achieve the status of a John Hinckley.

Mueller threw together the first draft of a script he called The Assassination of Richard Nixon and, urged on by an optimistic producer, sent a copy to Sean Penn. "I loved the idea of Sean being in it," he says. "Of course I did. But I was terrified that we would then have a five-month hiatus before his agent would phone back to tell us he couldn't read it."

Mueller needn't have worried. Three days later Penn phoned to say he loved the script and would like to meet the director.

The central role offers all those things that blood-and-sinew actors such as Penn savour - madness, pathos, a death scene - and the story possesses powerful momentum. But I wonder why the actor was so keen to commit himself to a young director working on his first feature.

"Well, I just took yes for an answer and didn't question it," Mueller laughs. "But that first meeting was obviously my audition. I guess I passed. He did tell me that he likes working with writer-directors, because he is one himself. He understands the problems. But ever since that meeting his support for the project was absolutely unwavering. And one benefit of the financing falling through all the time was that it gave us a chance to build up a very close relationship and work through the character."

While building that character, they studied transcripts of the deranged tape recordings that Byck mailed to various celebrities. The picture focuses most closely on the monologues sent to conductor Leonard Bernstein.

"When I was speaking at the National Board of Review, somebody stood up and said they could verify that this bit was true. 'I was a friend of the Bernsteins and I was there when the tapes arrived,' they said. That was not a happy day.' It must have been a very scary thing to be involved with."

Mueller's meeting with Penn took place in 1999. The director found himself with an admired script, a popular star and famous producers.What could possibly go wrong? Well, for some reason or other, by the autumn of 2001 a lot of the financiers had developed jitters about a project in which the anti-hero attempts to fly a commercial airliner into the White House.

"When 9/11 first happened, your first thoughts are, of course: how terrible," Mueller says. "But then you do begin to think: can we still do this film? It eventually occurred to me that now the film is now more relevant than ever we shouldn't just stick it in a corner and forget about it. However, financing was a different matter. Relevance often has an inverse relationship to how bankable something is."

I had read an interview where Mueller explained, intriguingly, that, before September 11th, he could have imagined circumstances in which the ending might have been changed, but that after the attacks he became less flexible.

"Yes, that's right," he says. "I could have changed it beforehand. If it was simply a practical issue - shooting in an airport is very expensive, for example - then that might have been OK. The mode of assassination wasn't so important. But then suddenly it became very important. In fact, I had, erm, financing entities say: we really want to make this film, but we can't make it with this ending. OK, they are still part of a big studio. I understand. But if I changed it now it would be a whitewash. I would be rightly lambasted by those who knew the original story."

These mysterious financing entities sound suspiciously like the pseudo-independent studios which operate within the majors: organs such as Fox Searchlight, Warners Independent and Miramax. Mueller smiles enigmatically. "Perhaps. I am certainly not going to name any names."

At any rate, The Assassination of Richard Nixon, whose roster of producers and executive producers includes such luminaries as Leonardo DiCaprio and the directors Alfonso Cuarón and Alexander Payne, ended up being made as a properly independent production. It is a taut, focused business which builds nicely to its inevitable calamity. That said, Penn, who really needs a strong director to curtail his instincts towards excess, allows all his acting meters to bounce in the red throughout. One wonders if Mueller had trouble controlling him.

"If caring as deeply as Sean cares about the work is difficult, then I will take that kind of difficulty any day. We had our disagreements, but they were always about the work. They always elevated the work. Is Sean difficult? What on earth do they mean?"

Well, Penn has demonstrated evidence of a sense-of-humour bypass recently. He didn't much enjoy his portrayal as a pompous blow-hard in Team America: World Police, and his huffy, pouty reaction at the Oscars to Chris Rock's mild comments about the ubiquity of Jude Law - Penn's costar on the upcoming remake of All the King's Men - showed him in a poor light.

"I would say he is one of the most fun guys to hang out with. He does a fabulous Irish accent. He has a great sense of humour. As far as the Jude Law comment goes, loyalty trumps what people think of him. I think he reckons that being loyal to his friend is more important than what people think of him. He's the guy you want to go for a drink with."

It is, of course, utterly unreasonable to expect Mueller, a Wisconsin-born graduate of UCLA film school, to diss the guy who helped launch his career as a feature director. Having received decent reviews for Richard Nixon, Niels, previously best known for cowriting Gary Winick's indie hit Tadpole, finally finds himself in a position of some power. But he confesses that one of his greatest pleasures was being able to use his father as a technical advisor.

The picture takes some liberties with the facts: Penn's Sam Bicke (the protagonist's name is spelt differently to that of the real assassin to establish some distance) begins the picture working as an office furniture salesman.

"He probably worked in a tyre company before he died," Mueller explains. "But we had him selling office furniture because he was obsessed with the American dream, and that way he came into contact with people who had lived it: self-made men, owners of small businesses.

"And my father had an office furniture store. He came down and showed us how to sit in order to secure a sale. So there is a bit of my dad in the film."

The Assassination of Richard Nixon opens today