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]

A gunman strikes down an Atlanta-area man in his SUV on the side of a motorway. Sheriff Investigators discover the victim is not well-liked among some in his inner-circle. But the killer eludes the law for 17 long years. [also shown as S6:E15]

On New Year's Eve in rural Pennsylvania, someone assaults and sets 23-year-old Ashley Kline on fire, killing her. The list of prime suspects includes her best friend, a jealous boyfriend, and a recently released prison pen-pal convicted of sexual assault. [also shown as S6:E16]

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]

On the sub-zero Canadian prairie, Royal Canadian Mounted Police discover a woman inside her hoarder home, a bloody ice-axe beside her. Her adult nephew lies frozen in the bed of his pick-up. Now, it's up to the Mounties to track down their killer. [also shown as S6:E20]

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]

As detectives reconstruct a single mom's final 24 hours, their suspicions turn to her fiancé, a creepy co-worker, and a violent ex-boyfriend. Ultimately, investigators discover a disturbing pattern of attacks -- and a predator with the master key. [also shown as S6:E23]

After Michigan detectives find a popular hairstylist stabbed to death, their suspects include the victim's landlord, her married lover and an aggressive ex-boyfriend; an unexpected call ultimately leads police in the right direction. [also shown as S6:E24]

Deputies in Tennessee find a beloved Memphis-area basketball coach murdered in his home. As investigators dig deeper into his closest relationships, they gradually unravel a homicidal web of deception, lies, and family honor. [also shown as S6:E25]

After Santa Barbara Police find a Ph.D. student shot dead on his doorstep, California investigators unravel a cold-blooded family plot that hinges on a single strand of DNA. [also shown as S6:E26]

On Easter Sunday in Agawam, Massachussetts, police find the body of a 24-year-old woman. With DNA in its infancy, it will take 25 years before a determined DA, advances in DNA technology, and a suspect’s plea can bring the case to its shocking conclusion. [also shown as S6:E27]