I was making a left turn and I had the green light but I still reached out to see if the car was coming on my left side but I couldn't see it because their was a big van at the light. And when I was makinga left turn a car poped out from behind the van and hit me...
And then I called the cops and the cops came and I told him what happened but he stated that he had the green light but we both don't have a proof... how can I find out if it was his fault?

Usually there's a possibility that where there are traffic lights they have a cameras there to record that kind of stuff but other than that the only thing that would get you close to a form of evidece is finding someone who has witnessed the crash maybe if you remember what that van looks like you could track him down or something...

I will point out that, even if you had the green light, you can't legally make the turn if you can't do it safely. If the van was blocking your line-of-sight, you may be at fault.

Also, it's not entirely clear what you were doing at the time of the accident, so I could be wrong.

Your description of the accident is unclear. Where was this van? Was the car in the oncoming lanes that you were crossing or what?

It sounds like you were making your turn not from the left hand lane. In that case the majority of the fault, if not all of it, is with you. However, if the car was oncoming and you didn't see it because of the van, you might be equally at fault.

But really, it shouldn't matter. Just report it to your insurance companies and they will handle everything.