In a proceeding pursuant to ORS § 138.510 to 138.680, events occurring at the trial of petitioner may be shown by a duly authenticated transcript, record or portion thereof. If such transcript or record cannot be produced, the affidavit of the judge who presided at the trial setting forth the facts occurring at the trial shall be admissible in evidence when relevant. When necessary to establish any ground for relief specified in ORS § 138.530, the petitioner may allege and prove matters in contradiction of the record of the trial of the petitioner. When the record is so contradicted, the defendant may introduce in evidence any evidence which was admitted in evidence at the trial to support the contradicted matter and may call witnesses whose testimony at such trial supported the contradicted matter. Whenever such evidence or such witnesses cannot be produced by defendant for any reason which is sufficient in the opinion of the court, such parts of the duly authenticated record of the trial as support the contradicted matter may be introduced in evidence by the defendant. A duly authenticated record of the testimony of any witness at the trial may be introduced in evidence to impeach the credibility of any testimony by the same witness in the hearing upon the petition. [1959 c.636 § 13]