FINALLY: Some well-written Superman.
Captain Marvel accidentally kills the assassin who murdered his best friend, Scott Okum. Superman's anger at the assassin's death is only exceeded by his fury at the way Billy Batson has been treated by the wizard Shazam -- left on his own to deal with powers he barely understands, isolated, living in squalor, emotionally scarred. Just a ten-year-old kid inside a superhero's body.
This is from Superman/Shazam: First Thunder, published in 2006.