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

When a 42-year-old woman is strangled to death and posed in an unusual way in her bedroom, detectives are on the hunt for someone who would have wanted to humiliate her after murdering her. A hidden 911 call turns the case on its head.

A 36-year-old woman lies strangled to death in her own home. Clues at the scene indicate she knew her killer well enough to let them in and that the resulting murder was spontaneous. Now, police race to discover who could want this mother dead and why.

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 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]

Early one May morning in 2012, a Kentucky pharmaceutical company employee stumbles upon the body of a close colleague. Someone has beaten this devoted wife and mother to death, and police must eliminate her coworkers as suspects, one by one.

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]

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.

Divorced soccer mom Paige Birgfeld's disappearance catapults her ex-husbands to the top of the suspect list - but when one of them provides a tantalizing clue about Paige's risky secret life, the number of potential culprits explodes.

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 St. Charles, Missouri, businessman dies violently at work, and police suspect it was a business deal gone bad. Then they discover several insurance policies plus a secret double life, and their investigation veers into a whole different lane.

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.

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.

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.

In affluent Colleyville, Texas, a bloody home invasion leaves the housekeeper dead - but police soon discover she was the intended target all along. Little did the sweet grandmother know just how many people were impatiently waiting for her to die.

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 Nebraska woman fights for her life against a brutal killer – and loses.

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]

A 911 call from a worried ex-boyfriend sends police to the Powder Springs, Georgia, home of Danielle Marshall. Once there, they find her shot dead in the kitchen. As the suspects multiply, it takes some police ingenuity to nab the 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.

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.

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.

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.

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]

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 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]

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]

A single mother's murder moves police officers to tears at the crime scene.

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]

When the badly decomposed body of Margarita Scott is found in the backseat of her estranged husband's missing SUV, investigators must interview everyone close to her to retrace her final steps.

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]

Snowplow King Randy Scheffield is found shot dead in his bed by his wife on the first snowy day of the season, and Ohio detectives look into Randy's business to establish a motive.

A couple vanishes from their Washington home just days before Christmas.

A two-bit Florida criminal is arrested while driving a stolen convertible that has blood in the backseat, and its owner, a 49-year-old hotelier named Sabine Musil-Buehler, is reported missing; the case expands to include a possible homicide

When a small-town Michigan couple is gunned down in their own home, footprints in the snow and loose lips will lead police to their killer.

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]

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]

Two young girls arrive home from school 10 days before Christmas and find their father dead; police narrow the timeline of the murder down to an eight-minute window before the girls walked in the door

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.

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]

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 retired man is horrifically murdered by an acid attack in Florida.

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.

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]

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