Let's say the officer killed the punk, either before the first victim or after the last one. The narrative would be police brutality and more hate for cops. He probably would have still been dismissed from his job and sued by someone. Maybe lose either way.
That's just a ridiculous fantasy. Sure, there would have been a few deviant retards trying to second guess the heroism, but 99.5% would have understood this guy was a hero, instead of the despicable coward he's proved himself as.