I watched this movie like 10 years ago so I don't remember much.

The main character is in a prison and he is a very nice guy. Then there is a riot and some inmates have some guns somehow and police shoots them from the window immediately and they are ready to bust in and kill everyone but our guy throws the guns out of window and says that there are no more guns left and the police don't believe him but the warden(or a guard) says that he tells the truth. And when the police ask how he would know, he replied that the main character had never lied to him in 35 years (thats the number I remember).

And it was probably a black and white movie made in 60s but I cant be sure.

It sounds like you are looking for The Birdman of Alcatraz:

https://en.wikipedia.org/wiki/Birdman_of_Alcatraz_(film)


Birdman of Alcatraz (1962) - IMDb (http://www.imdb.com/title/tt0055798/)

It sounds like you are looking for The Birdman of Alcatraz:

https://en.wikipedia.org/wiki/Birdman_of_Alcatraz_(film)


Birdman of Alcatraz (1962) - IMDb (http://www.imdb.com/title/tt0055798/)

Yes. This is it. I actually saw the name when I was searching for it but I was sure it didn't take place in alcatraz so I didn't know