While there were some excellent performances, and some brave attempts at excellent performances, the actors portraying the two main characters were the weak links in the film. Both Mark Ruffalo as Inspector David Toschi, and Jake Gyllenhaal as San Francisco Chronicle political cartoonist, turned true-crime author Robert Graysmith, seemed miserably miscast. Neither actor were of sufficient age to carry off their respective roles, and in the case of Gyllenhaal, he appeared to de-age as his charectars obsession with Zodiac began destroying everything in his life.
I have to quibble with this. While I agree that they didn't age Jake as effectively as they did Downey, Jr. and Ruffalo, he was indeed old enough to carry off the role. Robert Graysmith was 24 when the Chronicle received the Zodiac's first letter. Jake was 25 when he filmed this, and Toschi was in his 30s, as is Ruffalo.
There was very little in the way of flesh to his portrayal of Graysmith, which made it difficult to care about why he became so enthralled with the serial killer. Ruffalo faired better as Toschi, in part, because much of his performance was paired with the ever entertaining Anthony Edwards as his investigating partner, who eventually requests a transfer off the case and out of the homicide department. Stand out performances from Robert Downey Jr as the self-destrucitve Chronicle crime reporter Paul Avery, and John Carroll Lynch as the only real suspect in the killings kept me watching whenever they were on screen.
On this count, I don't think Graysmith has to have a reason for becoming obsessed with this case other than that he is an obsessive person. Why are all of us here (perhaps present company excluded?) obsessed with Brokeback Mountain? We've never really been able to find a common thread. It just moved us for some reason that can't always be quantified and here we still are.
I did read an interesting interview of Graysmith, though, where when asked whether he was a reporter at the time, he said something like he wasn't even a writer but a political cartoonist, and he was a political cartoonist partly because he wanted to be a painter and a sculptor and many of the great American painters had started out as political cartoonists and partly because he thought that by being a political cartoonist, he could change things with his art - he could have a politician removed from office, for example. He said that when the Zodiac's ciphers started coming, he was impressed by his artistic skill - how he had drawn all those symbols perfectly symmetrically spaced and sized without a ruler. And he was impressed by the idea that this man was using his artistic skill to scare people while he was trying to use his to help people.
Do you think if they had spelled all this out in the movie, you'd have understood his obsession better? To me, it was understandable. The problem I had with the performance, and it pains me to say this, was that I don't think Jake pulled off, as Jeremy Fox at Pajiba said, "the unnerving intensity of the truly obsessed." It bothers me that he didn't pull this off because I know he can. He did it in "Donnie Darko" brilliantly, and he did it in "Jarhead" as well. So why not here? I have to say I was disappointed in his performance because I didn't feel that intensity this time. He was good, don't get me wrong. He is always good. But he just wasn't quite at his best.