Harry Potter question?

My question is: did everyone in the Order of the Phoenix know that Sirius Black was innocent when he was sent to Azkaban for supposedly helping Voldemort kill the Potters? I know that Lupin knew, but what about Dumbledore and Snape? Because in the book Snape wanted to kill Black in the Shreiking Shack and Harry attacked Snape to prevent him from doing so. And Dumbledore was also so protective of Harry and the others to prevent them from being attacked by Sirius. Does this mean that Snape and Dumbledore don't know that Sirius is innocent? But aren't they all in the Order? Please Help!