thats the job of the professionals, to work out and assess which individuals show a tendency of violence and are likely candidates to commit offences.
if undecided then they should err on the side of caution and detain them. if no one can make sure they are taking the medication that keeps them placid they should err on the side of caution and detain them. the caution is to protect the public not the individual.
prison is there to detain those that willfully commit similar offences.mental institutions are there for those not in control of their mind or actions.both are there to protect the general public.