By the time you have that evidence, the evidence will be being carried out in body bags if there is a shooter.

"Perhaps the most notable aspect of the deadly force findings is that SWAT officers rarely discharge their firearms at human targets. We estimated that across the hundreds of team years for which we had data that SWAT officers took suspects under fire in just 342 of the tens of thousands of operations they undertook"

https://www.ojp.gov/pdffiles1/nij/grants/223855.pdf

I don't think that most SWAT responses are actually saving lives with bullets. Also included in that paper is a table showing that most frequently, SWAT is used to serve warrants.

I’m glad that most SWAT incidents end without the team firing any rounds. To me, that’s a success case and a better outcome than if the metric showed “50% of the time, officers discharged their weapons”. It’s not a waste when their body armor goes untested on a call either.

If a warrant serving situation seems dangerous enough to use SWAT, I hope they use them and no rounds are fired. That’s a good warrant service, not a failure, in my book.

Can you describe the process you are suggesting?

"After receiving a phone call concerning an active shooter situation, the force sent round a single officer, just to double-check. The officer was among the 7 killed by the gunman."

Remember the story of the boy who cried wolf? The sheep were slaughtered because the town stopped trusting him. I'd rather the police scare a few unlucky people and waste some resources than learn to distrust our cries for help. Of course it's a tragedy that someone lost their life, but how many lives would be lost through not mobilising enough police?

Do you think we need corroborating evidence of a fire before rolling a fire truck, or is a phone call enough there?

The difference is that the fire brigade don't tend to run into a house and shoot the occupants.

Well in the case that we are discussing here, the police didn't shoot the guy.