Of course, it is always possible that the shooter saw something he really, really liked in the Pottery Barn window (their summer tablescapes are stunning) and got so excited that he dropped his spare bullets. But you’re probably right, and it was shell casings.
Maybe they shot the pottery in the wondow for target practise and unintentionally struck the two victims? Good pottery target shooting is hard to resist.
But what is "the other evidence?" Maybe an empty magazine? A dropped bottle of eau de chance ( queer love triangle revenge)? A portion of uneaten pizza( the Italian mob factor). I feel a board game design coming on. I will have to stop this and have a bottle of Sierra Nevada ale.