(2) If the petition states a ground for relief, the court shall decide the issues raised and may receive proof by affidavits, depositions, oral testimony or other competent evidence. The burden of proof of facts alleged in the petition shall be upon the petitioner to establish such facts by a preponderance of the evidence. [1959 c.636 §12; 1996 c.4 §4; 2003 c.261 §4]