I think this is outwith the scope of Mudcat's remit.
While I sympathise, having had to deal with people who fit the paranoid description, to a T, I know how life destroying it can be, if you let it.
Seek professional help, if the person concerned is exhibiting dengerous behaviour, either to themselves or others, you may be able to get a doctor to have them sectioned. They will then be assessed by medical health professionals.