[Ditter]

What would the "low crime stats of Boulder" have to do with the rage that the boy 'might' have felt over his younger sister receiving ALL the attention?

[defenderSD]

The environment in which the brother grew up would have a significant impact on his response to any jealousy he felt about his sister receiving more attention. To some extent, children learn how to respond to events in life from the way people around them behave. So a child growing up in an area with very little violence would tend to be much less violent than a child growing up in a violent area (all else being equal).