mon introduces an interesting point. Show him how to turn a crisis where he feels victimized into a way to empower. That's a powerful lesson and one that creates a lot of good in the world. Looks like he's on his way with the book idea.
Also, every kid can have a bad day, and he's six, crying at six isn't unheard of in fact it's still pretty age appropriate. Especially when someone goes out of their way to hurt you by killing what he considered an innocent bystander, and then getting away with it by lying. It feels patently unfair and I can empathize. One of the things that drove me crazy as a child was people who behaved in such an uncivilized way, they weren't playing by the/my rules - and I needed them to play by the rules to feel safe.
That said, going back to his age, lots of kids in my DDs class last year cried at times, boys and girls. Don't forget he's only six.
