Basement scene, my thoughts
I've watched this film maybe about 6 times and always felt disturbed by this scene as many have.
But I'm watching again tonight and I realised, this is just some am-dram guy spooking it up. Graysmith wasn't a cop and he knew he had no evidence on him. It's actually a pretty funny scene and is telling when people accuse Fincher of blindly agree with Graysmith.
Guy was a crank.