Transformers Fanfics, Essays, Author Interviews and More...! Established 1996!
Optmus and the others are just so blinded by their own prejudices. Jazz is right. There is no evidence and they're just ASSUMING that it was Scavenger because he happened to be there. They don't even consider the possibility that he might simply have been an eyewitness, because of course it's "only Decepticons who do those things." They aren't taking a good look at their own behavior to see how alike they are to what they say the Decepticons are. Their anger and prejudice are blinding them.
Here's hoping Jazz and the others won't get caught. That he's willing to buck what the other Autobots are doing takes a lot of courage, and that is one hell of a show of faith.