Four members of the Mark family are found murdered in their Cedar Falls, Iowa, home, prompting police to suspect someone close to the family; the bizarre outcome shakes the townspeople and devastates the surviving members of the Mark family.

Ten-year-old Leona O'Loughlin fails to show up at school, while her detective father Leo falls violently ill; investigators consider the chilling possibility that someone may be trying to eliminate the entire family.

In Los Angeles, 1968, Cheryl Perveler is found bleeding to death in her sports car with a gunshot wound to the head, then investigators delve into Perveler's life and uncover an outlandish plot that defies belief.

The blood-soaked body of 76-year-old Franklin Bradshaw is found behind the counter of his auto-parts store, prompting detectives to dig into the strained history of his family and uncover a hotbed of deceit, manipulation and all-consuming greed.

Heiress Barbara Mackle is kidnapped and buried alive in a coffin-like capsule; local police and the FBI race to Mackle's abductor before her time underground runs out.

In what became known as the crime of the century, a boy from one of Chicago's wealthiest families is kidnapped and found murdered; the ensuing investigation zeroes in on the wealthy, thrill-seeking college students, Nathan Leopold and Richard Loeb.

Chicago is gripped with terror after three bizarre and savage murders go unsolved; police officers and newspaper reporters are eager to deliver a suspect amidst the public furor.

The story behind author Truman Capote's classic non-fiction novel, "In Cold Blood," which details the Clutter family murders in 1959 and the nationwide manhunt for the killers that followed.

In 1970, an entire family is discovered shot and drowned in their own swimming pool in Santa Cruz, Calif., and investigators must search psychedelic hippie communes to solve this Manson-style murder.

In Los Angeles, 1922, a man is found dead, while his wife is discovered locked in a closet, and detectives soon find themselves caught up in a world of seduction and obsession where the ghosts are all too real.

In Bronx, N.Y., 1941, tea for two ends in murder, and investigators must count on the testimony of a few brave women to bring the killer to justice.

Patricia Jones' bullet-ridden body turns up in a secluded spot in Kansas City, Mo., and Detective Browning trails her killer from Missouri to Mexico, taunted by the sly smiles of his arch nemesis.

In 1958, two love-struck, sex-crazed teenagers embark on a killing spree in Lincoln, Neb., and it will fall to one local sheriff to put the brakes on this nightmare of a joyride.

In 1961, police uncover a shocking high school rumor as they search for teenager Betty Williams in Odessa, Texas.

In 1934, Eric Madison is found shot to death in a boarding house at the back of the Warner Bros. lot, and his beautiful widow, Nellie, is convicted of murder and sentenced to death.

Marilyn Sheppard is found beaten to death in her bedroom in 1954, and it will take more than 30 years for investigators to piece together the truth of what happened the night she died.

In Macon, Ga., Mary Burge is found strangled in her bed, and detectives must delve into a world of hooded Klan members and Yankees in which truth is stranger than fiction.

In 1937, a pin-up model and two others are discovered brutally murdered on Easter Sunday.

In 1966, Richard Speck slays eight nursing students at a Chicago dormitory, while the ninth nursing student survives the crime of the century by hiding under a bed.

After a 28-year-old teacher for deaf children is murdered in 1973, detectives must immerse themselves in the swinging nightlife of New York City to solve the case.

In 1968, a Gaffney, S.C., reporter receives a telephone call from a murderer who threatens to kill again.

Chilling scenarios unfold in this true-crime series, which tells actual stories of people who shared their lives with loved ones who became killers. Each hourlong episode puts viewers in the shoes of the loved one, who first notices that something is amiss, interprets the puzzling signs and clues, and eventually comes face-to-face with the horrible truth: that the person has a very dark side. Exclusive interviews and firsthand accounts of the critical moments leading up to the vicious acts showcase devastating, often undiscussed consequences on the people who have nurtured, loved and raised a murderer.

From the outside, families seem like harmonious units in loving homes. But you don't necessarily know what secrets families are hiding from the outside world. This series, narrated by actress Brenda Strong, explores families hiding the most extreme of family secrets: murder. Each episode explores a death in a family, unraveling the motives of the family members, all of whom are potential suspects -- and potential victims. Sibling rivalries, disputes over family businesses and infidelity are some of the factors that lead to the families' ultimate betrayals.

How well do you know your neighbors? What are their names? What do they do for a living? After watching "Nightmare Next Door," you may want to find out a little more about them. Each episode tells the story of a murder that happened in a seemingly tight-knit community. Viewers get to the heart of the case through interviews with investigators, prosecutors, family members and -- of course -- neighbors, in addition to forensic experiments. The stories reveal twists and turns, and when a suspect emerges, the final outcome can surprise everyone involved.

From blushing brides turned cold-blooded killers to smitten grooms with shocking dark sides, "Fatal Vows" examines the criminal psychology behind deadly divorces. Guiding viewers through actual stories of love gone wrong are psychotherapist Stacy Kaiser and forensic/clinical psychologist Dr. Brian Russell, who examine each couple to better understand how the marriage turned from flawed to fatal. Stylized re-enactments are supported by interviews with family, friends, law enforcement, and potential victims of the crime, while Kaiser and Dr. Russell provide analysis on unions that break down until divorce and murder collide.

Veteran journalist Paula Zahn steps out of the studio and into the field to unravel criminal investigations, tracking the drama of each story by featuring the opinions of those closest to the case, including law enforcement officials, the families of the victims and the incarcerated, lawyers from both sides, and first-time TV interviews with convicted murderers.

Lt. Joe Kenda spent 23 years in the Colorado Springs Police Department, where he amassed a lifetime of memories catching killers and helping solve close to 400 homicide investigations. The vivid memories are brought back to life in this hourlong series, as Kenda reopens his "Murder Books" for viewers -- folders in which every detail of his murder cases is held -- to revisit the most disturbing cases still haunting him today. As he details the process of how he solved the crimes, Kendra also embarks on a personal journey, coming to terms with long-suppressed nightmares. As he says, "I don't want to tell these stories. I need to."

Dark dreams see the light of day in "Your Worst Nightmare," a typical Investigation Discovery true-crime series complete with jump-out-of-your-seat moments and chilling conclusions. Classic suspense film techniques highlight re-enactments of creepy, harrowing crimes, as victims' darkest dreams become unfathomable realities. Each hourlong episode features one story interlaced with commentary from law enforcement, criminal justice professionals, and psychologists, plus accounts from friends and family of the victim.