Mo. Rev. Stat. § 632.440
No officer of a public or private agency, mental health facility or mental health program; no head, attending staff or consultant of any such agency, facility or mental health program; no behavioral health liaison, registered professional nurse, licensed physician, mental health professional nor any other public official performing functions necessary for the administration of this chapter; no peace officer responsible for detaining a person pursuant to this chapter; and no peace officer responsible for detaining or transporting, or both, any person upon the request of any behavioral health liaison pursuant to section 632.305 or acting pursuant to the request of a guardian who is acting pursuant to chapter 475, or upon the request of the head of any supervisory mental health program who is acting pursuant to section 632.337, regardless of whether such peace officer is outside the jurisdiction for which he or she serves as a peace officer during the course of such detention or transportation, or both, shall be civilly liable for investigating, detaining, transporting, conditionally releasing or discharging a person pursuant to this chapter or chapter 475, at or before the end of the period for which the person was admitted or detained for evaluation or treatment so long as such duties were performed in good faith and without gross negligence.
§ 632.440, RSMo