Missouri Revised Statutes Title XXXVII. Criminal Procedure § 544.230. Officer not subject to arrest--posse

The officer or person having such prisoner in charge shall not be liable to arrest or civil process while on his route; and he shall have the like power to require any person to aid in securing such prisoner and retaking him if he escape as sheriffs or other officers have in their own county; and a refusal or neglect to render such aid shall be an offense punishable in the same manner as for disobedience to a summons to assist in the execution of process.