Someone is sending around emails falsely accusing my sexual molestation from over 20 years ago. It is 100% false and is causing me harm.

THe person doing this is a relative who is 7 years my junior and is my cousin sister's son. He is alleging that I molested him when I was a teenager (14-15) and he was around 6-7 years of age. This has come out of no where after close to 20+ years later and has totally shocked and upset our families. He has sent comunications to my wife and my brother and my sister in law and my father warning them to keep thier kids and my kids away from me. He is doing this all from out of the country while he has some sort ofsickness that is affecting him mentally and is allegedly taking drugs according to his brother. What can I do to cease this immediately as it is both slander and liber that he is committing.