The way they show it reduces crime* is by comparing periods of time.
So, first quarter this year to first quarter last year, or 2011, 2010, etc. to show a trend.
Just as when the anti-rights people challenge us to point to a crime we've prevented, it's nearly impossible.
Though in the case of the individual armed citizen is is possible to see criminals start their attack (case a restaurant, for example - see the Kennesaw Waffle House report) then decide not to continue.
I think that the questionability (if that wasn't a word, it is now) of the reports from MPD is in itself enough reason to deny funding for any program they clain reduces crime.
"program designed to inform local law enforcement's policing decisions"
Here I disagree with da Gov. They do use data from shotspotter to decide where to put more officers (which usually results in more arrests & fewer crimes being committed while they're there).
"it helps catch criminals"
No it doesn't. They can tell the area where a gunshot came from. That's all. It doesn't give them a video image, to show who pulled the trigger.
* if we can rely on the MPD stats, which they've proven we can't
According to reports (I think it was a newspaper investigation), MPD starts by refusing to take reports on some crimes, then downgrades some of the ones they do take so they look like less serious crimes