If he's going to court in the future you might see if you can give the judge a letter (the more letters the better) telling him that he has psychiatric problems and needs help. My family did this for a drug addict. They had a facility for inmates with drug problems and he was sent there. The judge did read the letters and he heard us.
I'm bipolar and during depressions I did ask for help. After over 10 years I'm finally on a mood stabilizer that works. My daughter is my support person when it comes to my mental health. There aren't many people who can tell me I need to see the doctor when I'm not well, I get very defensive. It's very common for the mentally ill to self-medicate. Another thing you can do is tell the police that he's mentally ill if he's arrested again. They might take him to the hospital for a psych evaluation.