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]

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]

A shooter guns down Cleveland's beloved fire department lieutenant on his driveway; as he fades away, 45-year-old William Walker tells the EMS as much as he can about the suspect who ambushed him. [also shown as S6:E13]

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 coworker finds Dr. Joseph Sonnier's body face down in the garage of his Texas home. Before long, the list of possible suspects includes the victim's girlfriend, a mysterious stalker, and a long list of jilted ex-lovers.

A late-night break-in at a Pennsylvania chain restaurant leaves assistant manager Terri Brooks brutally slain; when another female restaurant employee is murdered in a nearby town, detectives fear there's a serial killer on the loose. [also shown as S6:E12]

The shooting of successful paediatric dentist Kendra Hatcher in the gated parking garage of her Dallas condo spurs detectives to unravel a twisted plot as they chase a fugitive who ends up on the FBI's most-wanted list.

Holistic doctor Teresa Sievers looks forward to a television career on the horizon until someone bludgeons her to death in her Florida home; a random tip from an out-of-state police chief ultimately brings investigators face-to-face with the killer.

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]

The key to solving the toughest murders lies somewhere in the final 24 hours of a victim's life. Determined investigators must piece together events to reconstruct the timeline, unlock the motive, and ultimately close in on the killer.

In Connecticut, a motorway clean-up crew discovers a suitcase containing the crumpled remains of 24-year-old Valerie Reyes; as the list of potential suspects grows, solving the case may hinge on a portrait of the killer sketched by the victim.

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]

A college student's effervescent personality wins him many admirers on his Columbia, Missouri, campus right up until the day of his murder. As a police search for suspects, a tip leads them to someone with a lot to lose.

An enraged killer strikes down 26-year-old Alexandra Ducsay, an aspiring entertainer with a big heart and a blossoming career; slain inside her family's Connecticut home, her attacker uses her own dance trophy to bludgeon her to death. [also shown as S6:E11]

With two mortal gunshot wounds and tape residue on his wrists and ankles, it's clear 21-year-old Landy Martinez suffered before his death; detectives hope the victim's cell phone provides the critical evidence they need to close in on his killer.

A college student is strangled to death in her Bryan, Texas, apartment. Investigators are hard-pressed to find anyone who would want to kill such a bubbly and dynamic woman, but DNA discovered on the scene proves there’s at least one person who wanted to do her harm.

Sixteen-year-old Cassie Jo Stoddart is housesitting in a Pocatello, Idaho, neighborhood. As she watches movies on the couch, Cassie is oblivious to the fact that she's not alone. When she finally realizes that someone evil is lurking, it's far too late.

A killer stabs a beloved New Jersey woman 44 times in her home. Investigators have the culprit's DNA, but finding him will require an assist from the FBI, a media blitz and a random tip with details only the murderer would know. [also shown as S6:E9]

A diligent art student lies stabbed to death in bed. The ferociousness of the crime makes little sense considering the quiet co-ed has no known enemies. However, police soon meet someone whose secret hatred for her reveals itself as a night of pure horror.

When newlyweds Joe and Olga Connell are gunned down outside their Wilmington, Del., home, police investigate a sibling rivalry, a business partnership plagued by drugs, and an outlaw motorcycle gang.

A cold-blooded murder of a 39-year-old woman sends detectives in Oldsmar, Florida on the hunt for a killer, and their only clues are three letters written in blood and a pizza delivery.

On a quiet summer night in 2010, a killer shoots dead a wealthy La Crosse, Wisconsin, couple in their living room. Police look to their financially strapped children for the motive to kill, but a strange discovery may veer them in a whole new direction.

Niagara Falls detectives find 72-year-old real estate agent Bruce Firman bludgeoned to death with a pipe wrench in the home he shares with his estranged soon-to-be ex-wife; Bruce was also a serial monogamist with a long list of jilted ex-lovers. [also shown as S6:E10]