(4) This section applies to
murder committed before or after the commencement of this section.
(5)
However, this section does not apply where committal proceedings (or
proceedings by way of ex officio indictment) for the murder were instituted
against the convicted person before the commencement of this section. In such
a case, section 19 as in force before that commencement continues to apply.
(6) Nothing in this section affects the prerogative of mercy.