Oh, now come on. You surely can't tell me that you believe that that crime justified that punishment. If some teenager egged your car would you chase him down into an ally and shoot him the chest? There is a reason the cops are looking for the shooter now. Because he's guilty of MURDER. It's not sugarcoating what the kid did, but the type of justice you're talking about makes "an eye for an eye" look like warm n' fuzzy liberalism.
Your compassion for criminals and total lack there of for their victims borders on abetting.
Who knows what someone's fight-flight-freeze survival mechanism is going to lead to, short-term, once triggered -- that's why it's best not to mess with strangers.
Besides that, we don't know if the shooter realized the threatening event had completely passed. For instance, how many folks have come back from wars and upon hearing the sound of a car backfiring, they're immediately startled, and feel like they're in battle all over again, even if they haven't been in battle for 10, 20, 30 years or more?