There is absolutely no public proof that he has cheated.
There is plenty of circumstantial evidence, however: 1) the fact that both are of the same country; 2) the fact that several top players -- Pushover, Timinator, Math Wolf -- have stated their belief Arlecchino and alt are the same person; 3) that Arlecchino set a vacation on Warlight last evening (the time I first posted my accusation) for ten days, and will likely try to wait for this to blow over, which will not happen; 4) both accounts have used the same name in the past. His only real defense now is to somehow prove that someone else was using the account at the time of the tournament, which still violates Warlight law in that you are barred from sharing accounts with a third party. Good luck with that.
Also the forum is not the place for reports. Use the report function. Make sure there is proof in that report.
This instance of cheating is a serious violation of trust in the community. I see no reason to keep it private.