Factual error: In the scene where Lt. Exley arrives at the Night Owl after the murder, the patrol officer is wearing a Safariland velcro-fastened handcuff case on his left hip. That style of rounded cuff case was not introduced until the early to mid 70s.
Continuity mistake: Bud and Exley are sitting in their car talking - Exley looks OK. His lip and eye are almost healed and there's only a little black and blue on the upper part of his left cheek. Than in the next scene with Lyn he looks like he's been beat up again worse than before. (01:56:10 - 01:56:40)
Continuity mistake: In the scene where Lt. Exeley resets the clock, the first time you see the clock it is exactly 5 minutes after 2. When Exeley puts on his glasses to see the time, it is clearly only 3 minutes after 2 oclock! (00:30:30)
Continuity mistake: When Bud White pulls into the driveway at Pierce Patchett's house to question him about Susan Leffert's murder, the wind is causing a tree top (top center of the frame) to sway. Before Bud opens the car door, you can see the tree come to a sudden stop in a position different than that of the last frame. (00:37:40)
Revealing mistake: In the scene where Bud is holding the DA out of the window you can see a wire attached to the DA's legs to stop him from falling. (01:49:20)
Deliberate mistake: When White almost fights with Exley in the street and is pulled away, the public mailbox by the side of the road is all blue. Mailboxes back then were red on top and blue on the bottom.
Factual error: During the interrogation room scene, it is very bright in the room looking into the interrogation room, and it is dimmer inside the interrogation room. Although this would mean that the suspect would be able to see everyone watching as for him to just see a reflection, it needs to be bright his side, and darker the other side. True the glass could have been slightly reflective on one side, but the laws of optics still apply.