Forcible entry and detainer defined. - RS Mo. 534.020
     If any person shall enter upon or into any lands, tenements or other possessions, with force or strong hand, or with weapons, or by breaking open the 
doors or windows or other parts of a house, whether any person be in it or not, or by threatening to kill, maim or beat the party in possession, or by such words or 
actions as have a natural tendency to excite fear or apprehension of danger, or by putting out of doors or carrying away the goods of the party in possession, or by 
entering peaceably and then turning out by force, or frightening, by threats or other circumstances of terror, the party out of possession, and detain and hold the 
same--in every such case, the person so offending shall be deemed guilty of a "forcible entry and detainer" within the meaning of this chapter. 

Proof required of complainant. - RS Mo. 534.200
     The complainant shall not be compelled to make further proof of the forcible entry or detainer than that he was lawfully possessed of the premises, and that 
the defendant unlawfully entered into and detained or unlawfully detained the same. 

Ladlord may take possession, when--landlord liable, when, burden of proof. - RS Mo. 441.040
     If any tenant violates the provisions of section 441.020 or 441.030, the landlord, or person holding under the landlord, after giving ten days' notice to 
vacate the premises, shall have a right to reenter the premises and take possession of the premises, or to oust the tenant, subtenant or undertenant of any person on
the premises with the permission of the lessee, sublessee or underlessee by the procedure specified by law. The landlord shall have the burden to prove that the 
premises were being used for the illegal possession, sale or distribution of controlled substances under a petition filed for that reason, but the landlord shall not be 
liable for any damages resulting from the landlord's reliance on written notification to the landlord by a law enforcement authority that the premises are being used for the illegal conduct described in section 441.020. 

Landlord's unlawful removal or exclusion of tenant, liability-- interruption of services, landlord's liability. - RS Mo. 441.233
     1. Except as provided in section 441.065, a landlord or its agent who removes or excludes a tenant or the tenant's personal property from the premises 
without judicial process and court order, or causes such removal or exclusion, or causes the removal of the doors or locks to such premises, shall be deemed guilty 
of forcible entry and detainer as described in chapter 534, RSMo. 

2. Any landlord or its agent who willfully diminishes services to a tenant by interrupting or causing the interruption of essential services, including but not limited to electric, gas, water, or sewer service, to the tenant or to the premises shall be deemed guilty of forcible entry and detainer as described in chapter 534, RSMo; 
provided however, this section shall not be applicable if a landlord or its agent takes such action for health or safety reasons.