Gyllenhaal ponders Downey Jr: mad or genius?

CANNES, France (Reuters) - Jake Gyllenhaal compares acting with Robert Downey Jr. to playing jazz and says he had no fears about being upstaged by his flamboyant co-star in the murder thriller "Zodiac".

The film, in competition at the Cannes Film Festival, is based on the true story of the unlikely quest by Robert Graysmith, a cartoonist on the San Francisco Chronicle, to identify a 1960s serial killer known as the Zodiac.

Graysmith's character, played by Gyllenhaal, gradually moves to the centre of the picture but much of his time is spent jousting with the newspaper's dissolute crime writer Paul Avery, played with palpable relish by Downey.

"A very good, typical actor has about 25 really interesting choices and ideas within a minute. And then there's Robert Downey Jr. who has, I would say, 500 to 750 ideas," Gyllenhaal said after the press screening of the film at Cannes.

"Some people would call that madness. I would call that genius," he said.

"You're running around an actor and then they're chasing you, all of a sudden -- that's a wonderful thing where rhythms are all over the place, it's like playing jazz with somebody."

Downey's character, sarcastic and whining by turns, is a stark contrast to his strait-laced colleagues in the newsroom and he dominates the film until his drinking and general excess prove too much.

GRAND THEFT LARCENY

"Zodiac", which has already opened in the United States, has had generally positive reviews, despite disappointing audience numbers and Downey's performance has attracted special praise.

"His cast is uniformly splendid, but if the Zodiac killer got away with murder, then Downey ought to be charged with grand theft larceny given how often he steals his scenes away from his competent co-stars," the Hollywood Reporter wrote in its review.

"Zodiac's" recreation of the atmosphere of San Francisco in the 1960s and 70s is meticulous and it conveys a huge amount of information as the investigation tails off and Graysmith, who wrote the book the film is based on, carries on alone.

Gyllenhaal joked that director David Fincher told him for the first part of the movie he would be "an extra" and much of the film is centered on his deepening obsession with the case and the way it gradually takes over his life.

Fincher, who made his name with the dark thriller "Seven", said he had initially been reluctant to do another serial killer movie, but had been won over by the film, which described events he had lived through as a child in San Francisco.

"I don't think this is a serial killer movie, I think this is a newspaper movie," he said.

"It's not a process by which somebody dismembers other people. It's not that kind of movie. It's a movie about the search for some kind of truth, the human mind's need to make sense of something that's randomly chaotic," he said.