UPDATE, 1:13 PM: Another possibility in this matter is that sometimes officers carry backup weapons on the job, with the approval of their departments. This would be, perhaps, a firearm purchased personally that can be carried on one's person while on-duty. I asked SFPD about this, and Sgt. Michael Andraychak just informed me that this was NOT the case with these two officers. Andraychak says the officers do not have backup weapons registered to them. Also, no other updates on the investigation that he knew of.
It's a key piece of evidence in the controversy over San Francisco Police fatally shooting 19-year-old Kenneth Harding: a .380 caliber bullet. The medical examiner's office says that bullet is the same caliber as a cartridge found in Harding's jacket pocket, but different from SFPD weapons.
Still, in the last few days I've gotten a lot of messages (particularly in response to my YouTube video with SFPD Chief Greg Suhr) asking whether a .40 caliber gun could fire a .380 bullet. In other words, could the bullet that lodged in Harding's head been fired by an SFPD gun?