Mo. Rev. Stat. § 104.1018: Vesting of benefits, when — reemployment of member, effect of.

1. When a member is no longer employed in a position covered by the system, membership in the system shall thereupon cease. If a member has five or more years of credited service upon such member's termination of membership, such member shall be a vested former member entitled to a deferred annuity pursuant to section 104.1036, except as otherwise provided in subsection 7 of section 104.1024. If a member has fewer than five years of credited service upon termination of membership, such former member's credited service shall be forfeited, provided that if such former member becomes reemployed in a position covered by the system, such former member shall again become a member of the system and the forfeited credited service shall be restored after receiving creditable service continuously for one year.

2. Upon a member becoming a retiree, membership shall cease and, except as otherwise provided in section 104.1039, the person shall not again become a member of the system.

3. If a vested former member becomes reemployed in a position covered by the system before such vested former member's annuity starting date, membership shall be restored with the previous credited service and increased by such reemployment.