The son-in-law of accused Nazi war criminal John Demjanjuk blocked the testimony of a defense witness by threatening to sue him for breach of contract. Prosecutors wanted William Flynn, chief documents expert for the state of Arizona, to confirm he told a seminar that a Nazi identity card bearing Demjanjuk's name was not necessarily forged--as the defense contends. Flynn, however, refused to submit to cross-examination, saying he had been threatened with legal action in a U.S. court by Demjanjuk's son-in-law, Ed Nishnic. Israeli prosecutors at the Jerusalem trial said Nishnic will be investigated for possibly obstructing justice. The son-in-law, a Cleveland salesman, said Flynn was being paid by the Demjanjuk family to testify.