This is a pretty serious accusation. Just because he wrote a character letter does not mean he is actively involved in covering up a crime, that’s a gigantic leap.
his true character
And what would that be? A person who vouches for his friend? Someone who misjudged another person’s character, a mistake presumably you’d never make?
I think it’s fair to judge
No, you think it’s fun to judge and it’s your excuse to feel morally righteous and superior. You’ve made some accusations and backhanded disparagement based on what info? How is any part of it “fair”?