Whether or not the 'system' has shortfalls, it's his fault. If he's that mentally disturbed to be able to kill someone randomly, and especially a pregnant lass, then he needs to die, no two ways about it.
How could any organisation possibly predict what he was really capable of?

I have a lot of sympathy for people with mental disorders, but no sympathy whatsoever for him.

I can't even begin to imagine how her family feel right now.