A SCREENWRITING HOPEFUL CRAFTS A FILM WITH A HORRIBLE TWIST, BUT WAS IT SIMPLY HIS OWN PLOTLINE FOR MURDER? "SCREENPLAY FOR MURDER" TUESDAY, JULY 10 (10:00 PM, ET/PT)

Mark Twitchell was pursuing his dreams of being a filmmaker when he produced "House of Cards," a project about a serial killer who creates a fake online profile as a woman to lure in men and kill them. But was he also a killer? As 48 HOURS MYSTERY correspondent Troy Roberts reports in this updated broadcast, few would have expected the married father and "Dexter" fanatic would become part of a real-life murder mystery. The horror started when Gilles Tetreault arranged to meet a woman he met online - instead, he found himself face-to-face with a madman who set a trap to kill him. He survived, but Johnny Altinger answered a similar online dating ad and never returned from a rendezvous. Roberts speaks to Altinger's brother Gary, as well as Tetreault, who describes the terror he experienced that fateful night.