The death penalty shall be imposed in all cases in which it must be imposed under existing laws, except in the following cases:
1. When the guilty person be more than seventy years of age.
2. When upon appeal or revision of the case by the Supreme court, all the members thereof are not unanimous in their voting as to the propriety of the imposition of the death penalty.
For the imposition of said penalty or for the confirmation of a judgment of the inferior court imposing the death sentence, the Supreme Court shall render its decision per curiam, which shall be signed by all justices of said court, unless some member or members thereof shall have been disqualified from taking part in the consideration of the case, in which even the unanimous vote and signature of only the remaining justices shall be required.