It obsessed several individuals, one of them - a cartoonist - so much, that he went onto pen two non-fiction books on the killings, the investigation. And it also inspired filmmaker David Fincher to make a film called by the same name and based on the books.

The film screened at the Cannes Film Festival yesterday. Fincher's effort is one that is engrossing, enrapturing, shot with attention to detail, to maintain the era that was the seventies, and make it look very real. Costumes fit the times, the locations have been recreated to suit the 70s. There has been no effort to fictionalise or glamourise the times.

The story has obsession with a mission as the central theme running through the movie. The efforts of the various individuals to nail and nab the murderer over the years go to make the sub stories or sub plots. Whether it is the detectives David Toschi (Mark Ruffalo) and his partner William, or it is San Francisco Chronicle crime reporter Paul Avery (Robert Downey) or it is the cartoonist Robert Graysmith (Jake Gyllenhaal), their key motive is: pursue and capture the heinous murderer. In the process, they nearly destroy or destroy their personal lives.

Of all the actors Downey Junior shines bright, bringing absolute realism to his performance as the journalist who gets burned out by his own doggedness, wrong turns, and a not so cooperative administration. He has at times good moments with Toschi followed by confrontations when he goes to the press with a lead which probably takes the case in a wrong direction. He turns to alcohol, finally giving up his job to work at a lowly paper and goes to seed.

Ruffalo is also very believable in a downplayed performance. In the beginning he mumbles but then picks up speed as the movie goes along.

But for me it was Gyllenhaal who is the standout. First as the cautious and unsure but clinical cartoonist who has a penchant for solving quizzes and riddles, then transforming into an amateur detective pursuing a criminal and finally into a novelist who wants to get at the bottom of things, searching for every clue with a comb and in the process "look at the killer in the eye, in the face."

Which we presume he does finally.

A flaw with the film is its duration: 158 minutes of it. It could have been made shorter, some scenes and subplots could have simply been edited out. For instance, some 30 minutes of the film are spent on following a certain line of investigation. At the end of it all, the main players discover, the line was wrong. Despite its length, it continues to grip the audience and that is to David Fincher's credit.