In all cases in which the chairman of the board or any other member designated by the board has suspended the execution of a death sentence to enable the full board to consider and pass on same, it shall be mandatory that the board act within a period not exceeding 90 days from the date of the suspension order. In the cases which the board has power to consider, the board shall be charged with the duty of determining which inmates serving sentences imposed by a court of this state may be released on pardon or parole and fixing the time and conditions thereof. The board shall also be charged with the duty of supervising all persons placed on parole, of determining violations thereof and of taking action with reference thereto, of making such investigations as may be necessary, and of aiding parolees or probationers in securing employment. It shall be the duty of the board personally to study the cases of those inmates whom the board has power to consider so as to determine their ultimate fitness for such relief as the board has power to grant. The board by an affirmative vote of a majority of its members shall have the power to commute a sentence of death to one of life imprisonment.