Illegal activities
Cray was organizing illegal dog fighting in town and was the one who was poisoning dogs all over the place. He would give them pills that would make them better at fighting but would do a lot of harm to their system. Then it was just a matter of time before they would die.
Dog fighting is a serious crime and the police take it especially to heart because of the animal cruelty. Nobody wants to see two dogs put up against each other for sport, it is just a cruel and terrible thing to do to an animal. Cray needed to be taken down and his operation stopped at once.