Attorneys for Facebook and its founder, Mark Zuckerberg, say they’ve found “smoking gun” evidence on a New York man’s computer proving he made up his claim that a contract he signed with Zuckerberg in 2003 makes him part owner of the social network.

Facebook’s statements, the strongest yet in what’s been a testy case, are contained in court filings in advance of legal arguments scheduled for Wednesday. Each side has accused the other of withholding materials.