Howard Marks (Dramatic Irony)
During the first murder we see in the film, Howard Marks sneaks back into his house while his wife is canoodling with another man. He watches as they begin to get intimate, then sits next to the bed that they both get on. While we the viewer can see that Howard is in the room, the two lovers have no idea he is there, which creates an instance of dramatic irony.
Anderton is Leo Crow's killer (Situational Irony)
John Anderton is the best cop in the PreCrime division, the most competent and trusted man in the department. Thus, it is surprising and ironic that when they are looking at the Leo Crow murder case, John turns out to be the murderer. The viewer does not expect that John would be a murderer, as he is on the side of justice and such a fierce advocate for the efficacy of PreCrime.
Lamar Burgess is the villain (Dramatic Irony)
Before John Anderton has any idea, the viewer learns that Lamar Burgess is the evil mastermind who has set the conflict in motion. When Danny Witwer goes to talk to him about the fact that John's framing has something to do with Anne Lively, Lamar Burgess shoots him in cold blood. In this moment, we realize that Lamar Burgess wants to cover up the death of Anne Lively and is behind all of the conflict that's taking place. Meanwhile, John has no idea that Burgess is the villain, and still looks up to him as a father figure, which creates an instance of dramatic irony, in which we know more than John does.
Blind John (Dramatic Irony)
After his eye replacement surgery, John has to wear a bandage while he's in the doctor's apartment. He stumbles around the room and there are a number of things that the viewer can see that he cannot. For instance, on television is an episode of Cops in which he is the targeted criminal who is going to get arrested that evening, but he cannot see this. Additionally, when he goes to the fridge, he eats a moldy sandwich and then drinks milk that's gone bad, which he cannot see, making for a particularly disgusting instance of dramatic irony.
