The violence isn't very graphic but it is very disturbing and it is even more disturbing because it actually happened.
The kills shown in this movie are more disturbing than grotesque or gory. The suffering of the victims is very detailed and the scenes are very helpless and scary.
Unlike Se7en, this movie mostly shows the violence in the act and it is disturbing. Despite this there are only three instances of violence and the rest of it is implied through dialogue.
Two people are murdered in a car. Not graphic.
Zodiac's threatening letters are shown on-screen and talked about. He talks about his murders and threatens more. With one he includes a bloody piece of a vicitm's shirt.
Violence is exclusive to the first half of the movie and it's very infrequent. It is also disturbing and intense.
Unlike another David Fincher serial killer film, Se7en, this movie is not graphic in the slightest.
Two of the three violent scenes are extremely shocking and horrifying.
The kills are pretty disturbing, but never too bloody.
Someone is shot in the back of the head. We see the man slumped over later.
We see a photo of a dead woman on the ground (blood covers her clothing, she lies in a pool of blood and we hear that she was stabbed). (some blood)
We see a man with bloodstained hands. (nothing much)