I just reread this. First time around was late at night and the cleverness of it got past me. This time I realized why. You've placed the reader in the position of the police. We are unsuspecting. We find the narrator credible, above suspicion. And then, at the last moment, the gig is up. The most incidental of clues, a cat and photo, are your undoing.
Best part is, the cat, beloved pet, reveals the identity of her owner's murderer.
This is just perfectly crafted. And I missed it on first reading. Ah, well, such experiences serve to make us humble, which is always a good thing :)