High Quality Content by WIKIPEDIA articles! Within the limits set by the US Supreme Court in Tennessee v. Garner, authority to use deadly force in the line of duty is granted by state law to state and local law enforcement agencies. Individual agencies set policies and procedures regarding when and how to use deadly force. When deadly force is used within the prescribed manner, the killing is deemed a justifiable homicide. Some law enforcement agencies routinely investigate all uses of deadly force while others investigate only cases involving extenuating circumstances. Other causes of death to suspects include accidents and police brutality. When the circumstances surrounding a death are questionable, a state and/or federal agency may investigate.