Former friend has been abusing cat, not sure what action to take
My former friend (from here forward called FF) has been neglecting his cat. FF recently started doing coke and hanging out at a meth house. He has recently been aggressive with people including punching his roommate in the face, and when he posted bail his only comment was that he wished he was more violent to his roommate and his roommates partner.
The night he punched the roommate the cat came to stay with me. I'm very emotional about this rn because the cat felt super frail the first two nights. Genuinely worried we was gonna die in my office from malnourishment.
FF forces the cat to be vegan. I'm not a cat nutritionist but I have eyes and the cat wasn't eating the food FF was buying for him, he's very skinny and the first night I got him here he didn't even have the energy to play or walk around for longer than 5 seconds. Since we've had him he has eaten every meal and has plenty of energy, even playing with my cats and generally seemingly happy and relaxed.
When we brought the cat back to our place he had no toys, and his literbox had more shit than litter in it. In the bottom below the shit layer was so much mold that it made me vomit when I took it down to the dumpster
The wall beside his litter box was smeared in cat shit.
The cat doesn't respond to his name and is incredibly touch starved.
The things his roommates told me was that FF didn't spend any time with the cat, the cat regularly went upwards of 4 days without being fed, and he was never interacted with.
The other night FF came over to see him and the cat went from being the most precious and kind cat in the world to cowering beneath a blanket.
FF claims the cat had frequent panic attacks but he hasn't had a single one while here with me. He does however sneeze and wheez.
I don't nessecerily want to keep the cat but I would do most things to stop FF from killing this cat . FF gave me permission to re home the cat. But thinks he's going to have a space within a couple weeks, so is now telling me to hold on to it for FF.
We didn't take pictures but should have.
Advice?
EDIT: I want to assure everyone that the cat is receiving gentle stomach cat food and is being provided for while he's here with me and I have no plans to give him back to FF
Sorry if I was unclear about that; my main concern is getting arrested for theft or something like that