He's in jail. Now should I do?

If you honestly believe that he understands what he did wrong, then by all means, go see him. Not every guy in jail is bad. It seems like your friend made a few mistakes, as we all do. He just happened to make a few extreme ones that got him into the situation he's in. He's going to need support & a friend while he's in there. If you're still unsure, try writing letters back and forth for awhile. When you're in jail, any type of support helps.