since you asked for general information, i'll give you a little bit...look up the legal definition of "libel." In the U.S., it's written defamation...if it's true, it isn't defamation, and the burden of proof in this case would likely go both ways...you'd have to prove the events happened (presumably, the court case you mentioned would be sufficient to do so), and your opponent would have to prove it didn't and that his reputation/work relationships have been irreparably damaged by your letter. I'm just a layman, and this is just how libel works in the U.S....you do need to speak with your attorney about how it works in Japan.

