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 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]

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]

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.

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.

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.

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]

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.

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]

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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.

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

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.

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

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.

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.

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]

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 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

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