1. Yes, strange that they can't go through ATF....something is weird with that.
2. So, it was one of their weapons that was stolen ?
3. If anyone tried to deal it through legit channels the SN would throw a red flag immediately.
4. The lower was probably discarded and replaced with a "clean" one.
5. I purchased a lower recently, so am I a suspect in this Don Quixote dragnet ?
6. Chances are great that they will not recover it.

If it was a department weapon, they're extremely embarrassed and are trying to pull a rabbit out of their ass at the expense of the law-abiders.

About 6 weeks ago we had a COP officer leave a Glock in a public restroom.
Boner !