https://zbrojnice.com/2019/08/19/ana...ctive-killers/

The article mentions incidents around the world instead of just the USA. It makes a good point, one that I've observed when reading about some mass murder or attempted mass murder incidents, in that an armed first responder doesn't always have to completely neutralize the threat in order to be effective in reducing casualties. Sometimes merely interfering with the murderers actions can buy time for unarmed people to escape or take cover, while waiting for the police.