Section 153. In all cases of petitions for pardons referred to the executive council by the governor, where the petitioner is serving a sentence in the state prison, the executive secretary shall notify the attorney general, and also the district attorney who prosecuted the case, and they or their representatives may be present at the hearing on the petition by the pardon committee of the executive council, examine the petitioner’s witnesses, and present to the pardon committee full information as to the case of the commonwealth against the petitioner on which he stands convicted of the crime for which he is serving sentence.