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 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]

After being stabbed at his Marietta, Georgia, home, beloved son Mitchell Jones dies at the hospital. Mitchell is a popular gay man, so police have several potential suspects. It isn't until they employ a new tracking tool that the case breaks wide open.

A killer guarantees that a popular square dancer will do-si-do no more.

When a charming 33-year-old is gunned down outside his home, detectives must comb over every detail of his personal life, professional dealings, and extracurricular activities to figure out who could commit such a brutal crime, and why.

A 45-year-old yoga instructor is found gunned down on his front porch on a hot September morning in Tucson. With evidence of a burglary, detectives wonder if the victim interrupted the crime. The case proves much more complex when a witness steps forward.

A concerned husband fails to get in touch with his wife after an alarm is tripped at their house, so he calls on the police to check it out. Upon arrival, they find his wife dead and try to connect the dots between an earlier burglary and a love triangle.

A popular college student is found stabbed to death in her apartment the day after Thanksgiving. Detectives in Jacksonville Beach must piece together her last known movements to pinpoint the time of the murder, and then they must find her brutal killer.

When a body found dumped in a gritty Brooklyn neighborhood is later identified as criminal justice student Imette St. Guillen, detectives must retrace her final hours at a Manhattan bar to catch her killer.

Mary loves her 40-year marriage and her thriving chiropractic practice in Whitesboro, New York. Then, she falls ill at work and dies two days later. An autopsy points to poisoning, and a mysterious letter implicates someone close to her.

A former marine's death reveals a string of angry coworkers and irate exes.

After his contentious divorce, Josh Niles finds love with Amber Washburn. Josh’s kids join their new family in Sodus, New York, and life seems like a fairytale until a determined gunman shatters their happily ever after.

Retired mortgage broker Alan Helmick’s blissful life comes to a violent end while enjoying a cup of coffee at his country home in Colorado. He has no known enemies, but when police find a gun, it’s clear someone close to Alan is an expert in murder.