A family mourns the unexpected death of a beloved grandmother at Christmas, and while local police assure everyone that she was the victim of a tragic accident, some things about the scene don't add up.

In 1990, three sex workers are brutally murdered and left along the banks of the Spokane river. A serial killer was on the loose—and detectives had few clues. Animal hairs, fibers and a fingerprint were found, but for years the perp was never identified. More than 20 years later there’s a break in the case- and an arrest is finally made, but no one could have ever imagined who was behind this sinister crime.

A murder victim’s final moments are caught on tape; the crime scene looks like a clear robbery-murder. Text evidence at first points to a jilted lover. Soon, police identify a second suspect with a possible motive of deadly revenge. Forensic technology and DNA evidence combine in an attempt to make the case.

A deeply religious librarian, wife and mother named Gail Fulton is shot execution style in the quiet suburbs of Michigan. Surveillance video reveals it was trio of killers that took her down. Eventually, detectives get a break: a handwritten note. But will it provide enough clues to catch the mastermind behind this horrific killing?

He is a criminally charged sex offender and a murderer who attacks in a terrifying rage. This predator manages to evade capture for years, but he leaves a critical piece of evidence behind – his palm print. Detectives are determined to do whatever it takes to put a name and a face to the print.

51-year-old father and teacher Bill Sparkman is found hanging naked from a tree with the letters “FED” scrawled on his chest. With barely any evidence to work with, investigators turn to these letters for answers… which leads to a surprising conclusion that no one saw coming.

A single mom looking for love vanishes without a trace. Foul play is tragically confirmed when a large pickup truck toolbox opens to her body stuffed inside. Homicide detectives investigate men she matched on dating sites, another man she met at work, and finally, a lover with a secret and violent past.

The murder of a young teacher’s aide leaves a hole in the heart of her small community in Agawam, MA. As the rumor-mill about suspects churned, the actual perpetrator slips further away. But, generations of investigators and a scientific breakthrough leads to a shocking end to a tragic case.

A 20-year-old woman sets out on her bike and never returns; her body found just a few miles from her house in Snohomish County, WA, with a gunshot wound to the head. Years go by without any hard evidence or leads, until a new generation of investigators and modern technology breaks the case.

A mortally wounded woman crawls to call 911. Her ex-husband, who wants to be free of her, gets a hard look from police. But he says he has an airtight alibi for the exact time of the murder. The intricate forensic science of ballistics is brought to bear to and draws a direct connection to an unexpected conclusion.

In 1982, 37-year-old Navy lieutenant Lee Hartley is murdered while deployed out to sea. Cause of death? Arsenic poisoning. Investigators discover Lee had more than his fair share of enemies aboard the ship. But it takes years before investigators discover what really happened to Lee and who, ultimately, was behind this brutal murder.

A building manager finds the violated and lifeless body of a young woman in the bathtub of her first apartment. When questioned, an ex-con living downstairs lies to police. But the lies alone do not prove murder and the case goes cold. Then, a new forensic tool examines the old evidence.

An early morning house fire kills the only doctor in the small town of Iaeger, WV. An arson investigation quickly leads to the arrest of Jason Lively, the son of the doctor’s long-time nurse. But when Jason’s alleged accomplice walks free, the prosecutor is worried this might have been a miscarriage of justice.

A fire leads investigators to re-examine an unusual death, which meant digging up the victim who had been buried for years.

When a Yale student mysteriously vanishes days before her wedding, investigators comb a secure research lab for evidence.

Police make a shocking discovery when they open a suitcase found floating in a bay.

A woman is killed in a crowded parking lot in the middle of the day. It looks like a professional hit, but evidence unveils an elaborate plan.

Police race to find a serial killer terrorizing a small Texas town.

Cell phone forensics help investigators solve a murder in an upscale community.

After the brutal slaying of a young couple on a road trip, the victims' families begin receiving disturbing letters.

The unexpected and mysterious death of a health-conscious woman triggers an investigation into what killed her.

After a young mom is found brutally murdered in her home, investigators find startling clues on her cellphone that could lead to her killer.

Investigators think they know who killed a young woman, but the case goes cold. An amazing new forensic tool turns the cold case around.

A small community is shocked when a woman is shot and killed in a church. Police are left with few pieces of evidence and no suspects.

An insurance agent is shot execution style in his office in broad daylight, but the killer left no fingerprints and there was no murder weapon found at the scene… Then, investigators discover a critical clue invisible to the naked eye that cracks the case. (also marked as S1:E12)