just go to general setting > discussion and enter their IP address and user name into one off the boxes below. This person obviously cant show proof of his claims so this person is most likely a nut job. Trust, me, I had a few nut jobs, after you block them they might start e-mailing you, just block them there too.
btw, don’t post your email or IP address here. the moderator will most likely remove them for you but don’t do that again, it probably only helps a hacker get into your site.