Security camera footage, shell casings and a small but distinctive tattoo played pivotal roles in the arrest of a man suspected in at least six killings over the past two months in the St. Louis and Kansas City areas.

The St. Louis Circuit Attorney's office on Tuesday charged Perez Deshay Reed in the shooting deaths of two people in the city in September. Reed was charged Saturday in two other fatal shootings in September in St. Louis County. He is also suspected of killing two people in Kansas City, Kansas, and the FBI has labeled him a suspected serial killer.

Reed, who turns 26 years old We...