Two Aum Shinrikyo figures accused of being involved in the 1994 Matsumoto sarin gas attack took the witness stand for prosecutors at the trial of Aum founder Shoko Asahara Friday, but both refused to testify.Tomomitsu Niimi, 34, a key cult figure, said he cannot testify because he refused to comment on the case in his own trial. Former Aum chemist Seiichi Endo, 38, said he needs to discuss the case further with his lawyers before testifying.Niimi has been indicted in connection with 11 cases blamed on Aum, including the Matsumoto attack, the 1995 Tokyo subway nerve gas attack and the slaying of anti-Aum lawyer Tsutsumi Sakamoto and his family. Asked if he had heard of the Matsumoto attack, Niimi said flatly, "I refuse to testify."But prosecutors continued to question Niimi about his alleged involvement in the attack and about other cultists' role in it. Niimi remained silent, refusing to answer even whether he knew what sarin gas is. The witness occasionally looked at Asahara, who mumbled occasionally from the defendant's seat.For about an hour, prosecutors, Asahara's lawyers and presiding Judge Fumihiro Abe tried to persuade Niimi to testify over for matters that would not harm his own trial.Witnesses who are on trial have a right to refuse to testify if the testimony could incriminate themselves.Unlike other cultists who have left Aum and testified about cases blamed on the cult, Niimi has maintained his faith in the religious cult. He has expressed his faith in Asahara during his own session.Endo, who has been indicted in connection with seven cases, including the two nerve gas attacks, also refused to testify saying that he had yet to discuss the matter sufficiently enough with with his lawyers to testify on the incident.