I would advise against responding especially if you're considering legal action. All it will do is draw you into an unhealthy dynamic with this guy and lead to your own involvment being questioned by the authorities. It would be much better for you to block him and concentrate on keeping your distance. If he tries to make further contact simply record what he writes/does for legal purposes, otherwise ignore it. It really won't help matters in the long term to respond to him, it will merely feed him and make him worse.