What constitutes a seizure under the fourth amendment when a police officer uses deadly force against an armed suspect?

Apprehension by the use of deadly force constitutes a seizure subject to the reasonableness requirement of the fourth amendment. Tennessee v. Garner, 471 U.S. 1, 7 (1985). "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." Id. at 11-12.