The 1991 murder of a young girl in San Diego is investigated.

Detailing the crimes of serial killer Keith Jesperson, also known as the "Happy Face Killer."

The 1985 murders of a young military wife and two of her daughters are investigated.

The fifth season opens with a case involving a high-school girl who was murdered in 1985.

The murders of three Arlington, Texas, teenagers in 1985 and the subsequent homicide investigation are discussed.

The murder of a man in Maine is connected to a cold case.

There is no sign of a break-in when 13-year-old Mollie Pittman is attacked and murdered in the Orlando, Fla., home of family friends; it takes investigators 17 years to find out whether she knew her killer.

Investigating a daytime robbery at a nightclub in Arlington, Texas, that resulted in an employee's death.

A 1993 triple homicide results in the deaths of a Kentucky veterinarian and his family.

A young couple is gunned down on a lover's lane in Georgia; A husband and wife are shot to death in their suburban Chicago home before the killer sets the house on fire.

In Portsmouth, Va., a 16-year-old ballet dancer is assaulted and murdered in her home, and detectives must investigate her family members as well as her circle of friends.

When 10-year-old Katie Collman is murdered in a small Indiana town, a shocking confession catapults this crime into national news. Was Katie murdered to keep her quiet about something she saw? An unusual clue leads investigators to the conclusion.

A friendly night out ends in a shallow grave for a beautiful young woman and her killer evades police for decades.

In 1996, teenaged Joey Martin sneaks out of his bedroom window to watch a comet from a cabin in the woods-and disappears. Despite multiple leads, there is no sign of Joey until 2008 when a young detective uncovers the shocking story of Joey's fate.

Shortly before Thanksgiving, a Philadelphia suburb is rocked by the murder of 67-year-old Alice Hufnagle.

The 2001 strangling death of a mother of triplets in Puyallup, Wash., is investigated.

The crimes and apprehension of the Texas Bathtub Killer are discussed.

When a beloved matriarch is found murdered, her friends and neighbors come under suspicion as detectives investigate the first homicide in the small town of Hubbardston, Mich.

The hunt for burglars who killed a Lafayette, La., man the day after Hurricane Katrina hit the Gulf Coast is chronicled.

When San Diego Police Officer Kirk Johnson is found shot to death in his service vehicle, evidence points to a fellow law enforcement officer. Detectives reluctantly begin to investigate their own when an astonishing tip leads to an unlikely killer.

Investigating a 1997 quadruple murder in Bartow, Fla.

The 1995 death of a Chicago woman whose body was found on a Wisconsin highway is detailed in the Season 4 premiere.

The 1997 murder of Henry Caneva and the investigation that nabbed his killers are discussed.

Philadelphia investigators bring to light the obsession that drove a suspect to murder student Deborah Wilson, who was found strangled to death in a university computer laboratory without her shoes and socks.

A cold case involving a 1988 murder in Sunset Beach, Cal., is investigated.

In Fort Pierce, Fla., a tax attorney is found strangled to death, and detectives must scrutinize deadbeat tenants and delinquent clients while hunting for his killer.

A serial killer on the loose in Spokane prompts investigators to take a new look at an old clue.

When tycoon Andrew Kissel is stabbed to death in his Greenwich mansion, detectives are faced with a long list of suspects. Practically everyone who knew the victim has a motive for murder. Ultimately, a secret money trail reveals the guilty party.

The 1980 murder of a Colorado teenager is investigated.

When a first-year college co-ed turns up raped and murdered, it takes a freshman cop to beat the odds and catch a killer.

The murders of three women in three Iowa hotels between 1993 and 1997 and the investigation that nabbed the killer are discussed.

An elderly couple are murdered in their Oregon home.

A Georgia woman is murdered just before Christmas.

A video tape surfaces after a naval officer is raped and stabbed suggesting the victim may have been silenced to prevent a scandal.

A 1990s cold case involving a serial rapist in St. Louis is reopened.

Investigating the 1989 murder of a high-school student.

FBI office manager Melissa Mooney is found murdered in her home. After taking a hard look at several promising suspects, the case goes cold. Two years later, a reexamination of the case leads to an unlikely killer who was hiding in plain sight.

"Went 2 Talk 2 Rob" are the last words 15-year-old Becky Stowe writes before she slips out, never to be seen again. Did she run away or did her boyfriend Rob make her disappear? Two years go by before the truth about Becky is finally revealed.

Soon after Mardi Gras in Mobile, Alabama, an 18-year-old freshman is found shot to death in the woods behind campus. Detectives take a hard look at several suspects, but thirty years go by before a stunning confession cracks the case.

A hotel manager is doused with acid in broad daylight.

A March 2000 murder in Anchorage is investigated.

In rural Wisconsin, a local eccentric is murdered in his home; A serial killer targets the elderly in Lake Elsinore, California.

The 1994 murder of Missy Grubaugh is discussed.

The strangulation death of an 8-year-old girl in Ocean Shores, Wash., is investigated.

The 1980 murder of a California businessman's wife is detailed.

A young boy is killed in the middle of the night, and his own mother is convicted of the crime. Years later, an author investigates a convicted murderer for her upcoming novel, and gets a confession that re-opens that case file and eventually, sets the mother free.

The murder of a young woman in her Portland, Ore., apartment is investigated.

A 1997 murder in a California town is investigated.

In 1985, an LA County Sheriff is gunned down in his vehicle. Investigators drill down the slain cop's list of enemies with no results. In 1999, a multi-agency task force shines a new light on the old case, illuminating a culprit who defies belief.

The 1992 murder of a church deacon is investigated.

The murder of a gun advocate in Kentucky and the investigation that nabbed her killer are discussed.

When a college student is found murdered in his Arlington, Texas, apartment, investigators suspect the kindhearted victim's generosity may have led a killer to his door.

In 1984, terrifying screams pierce the Florida night. A day later, a woman's body is found, stabbed to death. Detective Larry Tosi faces a host of suspects, but when the killer is caught, no one will be more shocked than Tosi himself.

The 1982 poisoning death of a naval officer is investigated.

The leading advocate for the controversial science of cold fusion is beaten to death and investigators run the full gamut of suspects, from corporate executives to drug-crazed burglars, to find his killer.

The murder of a popular young woman in Lancaster County, Pa., is investigated.

Investigating the 1992 slaying of a Las Vegas woman.

A mother's tireless pursuit for justice in her son's murder leads investigators to find a crucial clue.

The murder of an 8-year-old boy sparks a decades-long investigation.

Investigators in San Diego search for a serial killer after six females are slain in 1990.

Recalling the 1994 murder case of a young mother who was beaten and left in a garbage bin.

The killer of a Santa Monica art teacher remains at large for years as police use every trick in their arsenal to finally hunt him down.