The Court has said that use of lethal force is permissible where "the officer has probable cause to believe that the suspect poses a threat of serious physical harm, either to the officer or to others[.]" Thus, "if the suspect threatens the officer with a weapon or there is probable cause to believe that he has committed a crime involving the infliction or threatened infliction of serious physical harm, deadly force may be used if necessary to prevent escape, and if, where feasible, some warning has been given."