Have witnessed multiple instances of cruelty and abuse toward a dog but only ever see them out walking. Please help.

There‘s this tall red haired guy with a German shepherd in my neighborhood (near Auraria) who is SO MEAN to his dog but I only see them when they’re out walking. I’ve seen him violently jerk the dog every time I see them (at least 5x) and have seen him kick the dog twice. I can’t take it anymore. Last time I saw it was 2 days ago and I still can’t get the image out of my head. If anyone knows who this person is and suspects abuse please get in touch. I’ve witnessed it.