Guys doing maintenance on the exterior of the building from a cherry picker noticed the bullet fragment - which was the back-half of the bullet - laying between the two panes. When the building manager showed it to me, I saw immediately it was a hunting caliber size. It had material like that of the exterior of our building embedded in the front end of its remnants, leading me to believe it might have struck the building before hitting the window. Nobody would've been targeting me specifically, as there's no way to know whose apartment is where from the nondescript exterior. Lining up the largest hole in the screen with the hole in the window produces an oblique angle that also included the smudge or whatever on the inner, intact pane. This had to have happened in the past couple days & had me thinking to a loudish sound I heard hitting the window a couple evenings ago, which I attributed to a bird strike; although I can't be sure that was when it happened. It's an interesting mystery of sorts. The building manager messaged the photographs to the police that live in our building for their opinion, & in all probability will file a report to facilitate insurance coverage, among other things.