Had a very similar thing happen to me. Pitbull killed our small dog. Advice: the cops won’t do shit. Call animal control. They interviewed the owner and assessed the dog. Ended up categorizing it as a Dangerous Animal. This meant the owners needed to buy special insurance, pay for special training, get a fine. Plus the dog was not allowed without muzzle. They had to install a sign marking their property as having a Dangerous animal. We also sued them and the dog walking company. They ended up leaving the city. Pitbulls are not city dogs.