The Watcher (2000)

David Allen Griffin is a cool killer- time and time again, he chooses a female victim, studies her for weeks till he knows her routine to the smallest detail, makes meticulous preparations using his forensic knowledge to gain entry when she's quite alone, subdues her and administers a long, torturous death. Joel Campbell got so frustrated by his failure to capture Griffin in LA that he quit the FBI, moved to Chicago and remains in psychiatric therapy, unable to function normally... (imdb)