Two days after Christmas a mass shooting terrorizes a small town; after killing two people and wounding many more the gunman is taken into custody; when police search for answers they uncover the worst family massacre in US history.

On Christmas Eve in a quiet town, elderly couple Bob and Idella Young are brutally slain at home; a bloody glove found at the crime scene has the killer's DNA, but no one matches the sample.

The Ortega family's annual Christmas Eve party is destroyed when a man dressed as Santa, wielding handguns and a homemade flame-thrower opens fire; detectives are led down a terrifying path that leads them to a sociopath.

A holiday is ruined when a couple is gunned down in their bed during what looks like a brutal home invasion, but police soon discover the true motive for the double homicide is a shocking tale of deception and betrayal.

New Year's in a tiny town, Joanna and Carl Dutcher ring in the year with their grandson, days later, they are found violently killed; the hunt for the killer leads police to a sinister group that threatens the entire community.

Firefighters respond to a house fire and discover three gunshot victims inside; authorities pursue the heavily armed murderer through Christmas.

Earl and Terry Robertson are found brutally murdered in their home just before Thanksgiving; investigating whether this is a holiday robbery gone terribly wrong, or a crime committed by someone the couple knew and trusted.

The holiday season screeches to a halt when six members of the Anderson family are discovered to have been gunned down in their home; detectives work closely with family friends to track down the shocking murderer.

A deranged shooter attacks a family Thanksgiving dinner, leaving four dead and even more wounded, setting off a massive holiday-season manhunt to catch the killer - before they can strike again.

Most true-crime shows let viewers know the identity of the victim right away, before working their way into revealing the identity of the perpetrator. That's not how things work on "Killision Course," which conceals all of the participants' roles until the episode's final act. While working toward the conclusion, each hourlong episode re-creates a murder case involving a victim, accomplice and killer. Stories often involve friends or lovers who commit crimes against people who once trusted them. It's all part of the road leading up to the big reveal, which is when viewers learn what role each party played in the fatal act.

No one would suspect that the perfectly manicured lawns with trimmed hedges and fences lined up like toy soldiers would harbor such a secret, but sometimes things are not always what they seem. "Buried in the Backyard" examines true-crime stories about unfortunate victims found buried in the most unlikely of places -- the backyard. When the remains are unearthed, its the very beginning of an investigation, police piece together the person's identity and determine the cause of death before seeking the person responsible. Thrilling and captivating re-creations paired with firsthand knowledge from those closest to the victims can be seen as investigators track down the "why" and "how" and give viewers a shocking tale.

Some of the world's most notorious murders are the subject of "It Takes a Killer," which investigates the crimes from the perspective of the killers, trying to get inside their minds and determine their motives. Leading homicide investigators and experts from such agencies as the FBI and Scotland Yard take a look at the evidence pulled from crime scenes and profile the killer's behavior to try to piece together the details of each murder, explaining when, why and how each criminal committed the crime. For the wannabe detectives watching the show, the experts also reveal how the crime was solved -- which often requires authorities to think like a killer.

Marriage is supposed to be a happy time in a couple's life. With engagements, weddings, and picturesque honeymoons -- hope and happiness were in abundance until a tragic and very mysterious death occurs to cut short these joyous celebrations. Viewers learn when the red flags first began -- was it because of depression or manipulation and did it overshadow a wonderful time? Is it because of prophetic dreams and the killer was fulfilling a divine mandate, or is there something lurking beneath the surface that no one knew about.

Social media was in its infancy in 2004, but the explosion in its popularity in the years since then has kept alive a missing-person case. Nursing student Maura Murray vanished in February 2004 after witnesses heard what sounded like a car crash. The case has led a legion of armchair detectives to come up with their own theories about the apparent crime on blogs, websites and podcasts. In this series, investigative journalist Maggie Freleng tries to unravel a slew of unexplored leads, eyewitness discrepancies and missing evidence that have cropped up online. She receives rare access to Maura's family and friends and talks with people who have dedicated countless hours to searching for the truth in the case. Freleng retraces Maura's last-known steps to try to find out what really happened and tackle the unanswered questions that remain -- perhaps most importantly, did Maura choose to disappear or was she a victim of foul play?

"How do I solve homicides with no bodies, no evidence and no forensics?" asks special investigator Karsten von Hoesslin, who found himself in such a predicament while trying to piece together the truth behind a quadruple murder at sea. In 2014, cellphone footage from a mysterious address in Fiji goes viral. The 10-minute clip shows four men clinging to wreckage in the middle of the ocean. Then, one by one, the men are brutally shot and killed. No one knows exactly where it happened, why, or who committed these crimes. In "Lawless Oceans," von Hoesslin relentlessly pursues clues and angles, tracks down and interviews eyewitnesses, material witnesses and families of the victims, and seeks the support of fellow experts to determine who is responsible. Along the way -- painting a dark, grim picture of lawless international oceans -- he encounters drug smuggling, people trafficking, illegal fishing, and piracy.

Oxygen's long-running "Snapped" true-crime series takes a look at cases involving women who are accused of murder. In "Snapped: She Made Me Do It," women are the supposed masterminds behind deadly acts, but aren't necessarily the ones accused of the crimes. As is customary with these types of shows, witness testimony, interviews with experts and dramatic reenactments are used to tell the story of each case. Viewers get both sides of the story in each case before finding out the jury's verdict. Romance is often at the core of the attacks.

Oxygen's long-running true-crime series "Snapped" tells stories of people who commit murder or attempt murder, with the cases usually involving a woman trying to kill her partner. This extension of the franchise shifts the focus to couples who commit crimes. Using re-creations and firsthand accounts, each episode digs into a case, telling the story of the couple's romance, how the relationship evolved from love to manipulation, and what ultimately led the couple to commit the crime. The stories range from teenage lovers who go on a multistate crime spree to lesbian lovers who want to eliminate one of their husbands.

The first three days after somebody is abducted are extremely important. Statistically, the chances of finding the abductee alive diminish significantly after the first 72 hours. "Three Days to Live" chronicles kidnapping cases, using re-creations and first-hand testimony from authorities and loved ones to illustrate what went on -- from the crucial periods early on in the cases, which all feature females who were taken, through the twists and turns the kidnappings took before reaching their conclusions. Journalist SuChin Pak narrates the hourlong series.