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.

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.

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

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.

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 young Iowa man is shot dead while he sleeps peacefully next to his fiancée. Investigators wonder how she remained unharmed, and suspicion quickly swirls around her and two of her ex-boyfriends.

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 the body of 43-year-old Tina Coronna is discovered in the backseat of her abandoned truck, detectives must piece together clues gleaned from the victim's emotional husband, his mistress, and a neighbourhood vigilante

A woman is gunned down in her garage after finishing a shift at work and investigators must search in vain for a motive in the brutal murder. When her boyfriend finds notes she wrote prior to the crime, the case is flipped on his head.

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

A car explosion outside a Tucson country club leaves a business tycoon dead. Detectives determine the killer detonated the homemade bomb at close range, and the list of suspects soon includes mobsters, defrauded investors, and the victim's ex-wife.

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 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 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 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.

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.

A 27-year-old law student is reported missing, and when investigators later find human remains in the trash can behind her apartment, it's undeniable that the two are related. Police in Macon, Georgia, must act fast to catch a cold-blooded killer.

A 30-year-old woman is reported missing by her concerned husband after she fails to report to work. When her abandoned car is found, traces of blood in the trunk indicate more than just a disappearance - it's clear she has been murdered.

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

The murder of a beloved father days before Christmas shatters his family.

A 42-year-old Russian woman living the American dream in Texas is savagely gunned down in her garage. As investigators work the case, the list of suspects includes her controlling ex-husband, her boyfriend, an obsessive admirer, and a generous mentor.

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.

A popular Wisconsin funeral director and his intern are murdered in cold blood. The case stalls for two years before a criminal profiler takes a fresh look and sees only one viable suspect -- someone the police never considered.

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.

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.

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.

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.

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.

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 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.

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

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.

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.

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.

Gary and Jan Tyrrell are avid collectors of gold and silver coins and artifacts. Then they turn up dead, and investigators must find out exactly who knew about their expensive hobby - and who would be willing to kill for it.

In Tulsa, Oklahoma, taxi driver Rafael Hernandez's community reveres him as a caring and generous entrepreneur. Then, police pull his cab from a local river with Rafael inside, and the race is on to find his killers before they strike again.

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.

In Austin, Texas, a concerned son finds his beloved music teacher mother murdered in her bedroom. Within days, the victim's neighbor comes forward with some chilling evidence. Then, two more homicides convince police that a serial killer is on the loose.

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.

High school Freshman Tina Faelz ditches detention and heads for home - but someone murders her along the way. Suspects are plentiful, including a known sex offender, but decades pass before two determined detectives finally deliver justice for Tina.

A single woman hosts a dinner party on the same night she's mercilessly stabbed to death. At the scene, police notice her signature waist-length hair is cut short, leading them to suspect the killer not only knows the woman - but is obsessed with her.

In Brooklyn's Hasidic community, Menachem Stark enjoys life as a respected businessman and father to seven children. In 2014, his wife calls police when he fails to return home, and a subsequent search leads to a burning dumpster that holds a dark secret.

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.

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.

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.

A Tennessee college student returns to campus to find her friend and roommate Heather Maples viciously strangled in her bed. The outgoing co-ed has many friends, but police fear that on August 7, 2015, one of those pals turns out to be her worst enemy.

The beating death of a 15-year-old girl in Draper, Utah, outrages her parents, who had adopted her five years prior. One witness implicates a local drug dealer and another a mysterious gang member, but it seems almost everyone is lying.

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

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

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

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.

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.

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.

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.

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.

After a public health nurse vanishes without a trace, Anchorage, Alaska, investigators get a major break from her terrified neighbor; the race is on to recover evidence before it disappears under Alaska's winter snow. [also shown as S6:E7]

When the body of a single mother turns up in a snowbank outside Anchorage, Alaska, the evidence points to the victim's fugitive fiancé; the shocking murder of a second native Alaskan sparks investigators' fears that a serial killer is on the loose. [also shown as S6:E8]

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]

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]

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]

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 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]