Mo. Rev. Stat. § 70.695
The right of a person to an allowance, to the return of accumulated contributions, the allowance itself, any allowance option, and any other right accrued or accruing under the provisions of sections 70.600 to 70.755, and all moneys belonging to the system shall not be subject to execution, garnishment, attachment, the operation of bankruptcy or insolvency laws, or to any other process of law whatsoever, and shall be unassignable, except as is specifically provided in sections 70.600 to 70.755; except that:
(L. 1967 p. 141 § 20, A.L. 1988 H.B. 1098, A.L. 1992 H.B. 1440)