Dear Sir,
Normally when a matter is settled and damages are paid, the side paying damages will demand as a condition of payment that the other side sign a waiver of all future causes of action and any rights to further compensation or damages. Once the other side has signed a settlement document like this, it is very very difficult for them to mount any further action because they have given an undertaking to avoid it. Also, any action he mounts will need to be proven in court and if it simply cannot be proven by reference to physical evidence, the evidence of witnesses and documents then the case will not stand. Lying to a court is a very serious offence offence know as perjury which can be punished by imprisonment or large fines. Also, I am not sure if you are aware of this, but hearsay is not normally admissable as evidence in court. I think your best solution is negoiate your way into a position where they sign a waiver similar to the one I described above.
Regards,
David Coleman
This message is not legal advice and is given for informational, research and publication purposes only. No client lawyer relationship created. No liability incurred for use of this information. Thankyou for your business.