I watched this freaking brilliant movie last night, at 3 AM in the morning, when you can hear creepy sounds from the street and every little movement scares you out of your wits. 
I shriveled at some points, Got cold Several times. Believe me, the successive killings were no easy to watch. 
That’s how a brilliant movie influences on you. 
Also the pacing, the way Fincher puts information on your mind, or some scenes to again Make you unsure,  is unbelievable. 
The creepiest thing is that the Zodiac killer case is real. 
Anyway, beware that the rest of this: 

“CONTAINS SPOILERS “
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There’s a scene, where after Zodiac has the conversation with Melvin Belli on TV, 
The police call David Faraday to identify Zodiac’s voice. when he  Leaves the room, we see him limping, which was a Zodiac’s sign.
Yes, He was limping because of being stabbed by the Zodiac but for a moment there I thought what if He ,himself, was the Zodiac and he hired someone to make that scene and kill Betty (because it seems like the Zodiac kills only women in the double murders). 
You might ask why would he hire somebody to stab him? (that brutal!)
The answer is he is not mentally alright, so it’s not unlikely for him to change the killing pattern even if he get’s hurt in it. Also Betty mentions that he has a master in sociology. Maybe he ended up being a killer because of knowing much about humans and his comprehension of wild Human inclinations and stuff.  Not to remind That the Zodiac believes  “human is the most dangerous animal.”

Don’t know wether Fincher put the limping scene in order to distract us or it was just ordinary for david to be limping after being stabbed.

Anyway, 
I’m gonna focus on my real question: 
WHO THE HELL WAS THAT BASEMENT MAN, BOB VAUGHN?!!!
Was that supposed to show even though everything show’s that the Zodiac is Leigh Allen, it has never been proved? 
Even so, why did Graysmith just let it go? 
He was confused when he found out that Leigh was the prime suspect but his handwriting’s never been sampled!
How come he let go of Vaughn when he was likely to be the Zodiac? 

was the movie implicating that the Zodiac is most likely to be Leigh Allen, or that although all the evidence shows that it’s him, there are still other suspects such as Vaughn? 

But there’s still the scene in the store where Robert stared in Leigh’s eyes, as though he was saying “I know it’s you”
As he mentioned before, that his purpose in finding the Zodiac is to look him in the eyes (Like the way he did in the store) and be sure it’s him. 

So maybe this is the deal: Graysmith, Toschi, and Mageau conclude that the Zodiac killer was Arthur Leigh Allen. The film does too, But that’s still not proven. 

That the Zodiac killer case,
Is still open.