Sounds like they are looking for TWO guns here. A smaller caliber revolver is commonly carried as a "backup gun". Screening the LEOs .40 cal Glocks and backup guns sounds like a very reasonable angle. I wonder what the smaller caliber bullets yielded in terms of the rifling (twist, twist direction, number of grooves/landings). That is usually pretty manufacturer specific too...and MUCH harder to ditch compared to the typical barrel on a Glock.
I won’t post how it’s done but changing the impressions a barrel leaves on bullets is a very simple thing to do. I guess this is where we say thank goodness criminals aren’t known for intelligence.
I don’t remember the closure percentage rates for homocides nationwide but IMO it’s not that impressive. When you work under a budget you aren’t going to solve every case.