A gunman kills volunteer police officer Laura Grillo in her suburban Dallas home. Investigators must link a bombshell accusation to a game-changing email with a diabolical mastermind who thinks he can outsmart the law. [also shown as S6:E14]

In an affluent New York suburb, killers torture and beat millionaire Ben Novak in his hotel room; detectives soon discover that the businessman had many enemies, but one above all is the sadistic mastermind. [also shown as S6:E17]

Bookkeeper Barbara Iske fails to arrive on time at the Michigan home of her wealthy client; five hours later, she's found executed in the driveway of that same client; ultimately, police reveal that Barbara's the victim of a dark family conflict. [also shown as S6:E18]

Devoted father and aspiring boat captain Tray Phelps takes his last breath, murdered just steps from his front door; with no immediate leads, it's up to Missouri investigators to find the murderous manipulator at the heart of a sordid family plot. [also shown as S6:E19]

When Florida investigators find a retired Marine beaten then slain by a shotgun blast in his home, their suspect list grows from his estranged son to a mystery woman he'd just met -- to a possible serial killer. [also shown as S6:E21]