In the case of a person serving life imprisonment for murder of the first degree pursuant to § 18.2-32, the final deliberation and vote of whether to grant such person parole shall be attended by a panel of four or more members of the Board. In all other cases, the final deliberation and vote shall be attended by a panel of no fewer than three members of the Board. The Board shall promulgate rules to ensure that such members are randomly assigned to panels and to serve on an equal number of panels, as is reasonably possible. A decision to grant discretionary parole shall require the concurrence of a majority of members present for the final deliberation and vote, except that in cases of a person serving life imprisonment for murder of the first degree pursuant to § 18.2-32, a decision to grant discretionary parole shall require the concurrence of four or more of the members present for the final deliberation and vote.