Mo. Rev. Stat. § 115.599: Parties may subpoena witnesses and take depositions.

In all cases of contested elections, primary and other, the contestant and the contestee shall be allowed process for witnesses, and either party may take depositions, as in civil cases, to be read as evidence at the trial, as is authorized in civil cases. All such depositions shall be filed before the trial is commenced, and may be read in evidence no matter where the witnesses reside.