Mo. Rev. Stat. § 138.480: Papers may be destroyed, when.

The state tax commission is hereby authorized to cause to be destroyed, by burning, in the presence of the state tax commission, the papers herein designated, after a period of five years after the filing thereof, to wit: All tax returns of all individuals, firms, partnerships, and corporations; provided, that no such returns shall be burned as long as any tax based thereon shall be in litigation, or unpaid.