Do some digging into laws and ordinances in your city. There is probably something on the books against harming cats...roaming and feral. Where I live it is considered a felony. http://www.straypetadvocacy.org/PDF/AnimalCrueltyLaws.pdf
Perhaps some random flyers could reach this individual, persuading him to cease.
Perhaps some random flyers could reach this individual, persuading him to cease.