An exploration of the 1999 attack at a high school in Littleton, Colo., and the myths that may have inspired the active shooter phenomenon.

A white supremacist's deadly attack on a Sikh temple in Oak Creek, Wisconsin and the heroic response by local police, transforms a community.

A shooter's violent path through Santa Monica, Calif., leads to a deadly confrontation on a college campus; an examination of the shooter's mental health.

A community is left devastated and traumatized by the shooting at Pulse Nightclub.

Stories of loss and heroism during the 2013 shooting at the Washington Navy Yard; the shooter's sister recounts her brother's descent into violence.

The city of Charleston, South Carolina is ripped apart by a shooting at a historic church; in the aftermath, the community is divided by the idea of forgiveness.

The 2015 shooting in San Bernardino, Calif. brings out a massive response from law enforcement, while a shocked community responds to homegrown terrorism.

Survivors and first responders recount the 2012 movie theater shooting in Aurora, Colo.; a grieving family challenges the media.

The holiday season between Thanksgiving and New Year's is often thought of as a celebratory period to spend time with friends and family. That is not always the case, though, as the period is not immune from experiencing the same types of violent crimes that occur throughout the year. This series documents stories of tragedy that struck during the holidays, with firsthand accounts from people who had friends or family members killed during the joyous time. Sometimes the victim is killed by someone close to them, such as a case of sibling rivalry turned deadly, but sometimes the killing is done by a stranger who interrupts a holiday gathering with gunfire.

Each episode of this true-crime reality series examines a different felon, usually a female, who has committed murder or attempted murder. The victim is usually the perpetrator's partner. The documentary-style series features interviews with friends and family members of the accused and victims, law-enforcement officials, attorneys and other people with first-hand knowledge of the cases.

British journalist Piers Morgan travels to the U.S. to meet some of America's most notorious female killers. Hoping to discover what drives these women to commit unspeakable acts, Morgan delves into the details, meeting with family and friends from both sides of each case to find out how lives have been impacted and to gain an insight into whether or not justice has been served. He also talks with law enforcement, defense attorneys and prosecutors, often returning to the very scene of the murders. However, it's one particular chilling encounter that carries each story, as Morgan conducts a compelling interview with the killer inside the maximum security prison she calls home.

The stories in "Surviving Evil" are about actual crimes and people's will to fight for life and find courage when all hope seems lost. The victims of the horrific incidents describe what they experienced when they found their lives in the hands of cold-blooded predators, including how they summoned the strength and fearlessness to turn the tables on the assailants in order to stay alive. Actress Charisma Carpenter, best-known for her role on "Buffy the Vampire Slayer" and its spinoff, "Angel," hosts the 10-episode series, providing viewers with a first-person point of view as the survivor of a nearly fatal crime when she was 22.

Retired NYPD Detective Kevin Gannon questions if the country's most notorious string of mysterious, accidental drownings are accidents or homicides and wonders if they could all be connected to The Smiley Face Killers.

"Betrayed" reveals chilling stories of chasing the American dream and how the veneer can dramatically crumble, ending in murder at the hands of a trusted family member, co-worker, lover, or friend. The cases of deception are told through the lens of the fictionalized, first-person perspectives of the victims. As investigators, family, and friends peel back the layers and facts of each case, the otherworldly narrator already knows where the trail ends. The narrator guides viewers through various relationships, raising suspicions about who will commit the ultimate betrayal.

Continuing its quest into unusual true-crime stories, ID offers the documentary series "Evil Twins," in which each crime involves a set of twins. Sometimes the twins are both on the wrong side of the law, sometimes the twins turn on each other, and in some cases, they turn on their family. Each episode chronicles the events that led up to the crime, sometimes going as far back as the twins' birth. From a set of twins who work together to kill their father to brothers whose criminal lifestyle leads them to turn on each other, their stories are real, raw and disturbing.

"Relentless With Kate Snow" takes viewers on an emotional journey with grieving families as they work tirelessly, often putting their own lives in danger, to find the culprits responsible for the deaths of those they loved most. Their relentless pursuit of justice paired with the opportunity to work alongside law enforcement creates a powerful and dynamic force that won't rest until due process is served. From a mother dedicated to putting her son's killer behind bars after he's gunned down at a recording studio to a 20-year search for a victim's killer that was so aggressive it transformed an unsolved, cold case into an active investigation, the series reveals gripping firsthand accounts from the families who will stop at nothing to get the justice the victims deserve.

There are manipulators in the midst, scheming right under everyone's noses. Even with people trusted the most, there may be something sinister lying beneath the surface -- a plot set in motion by someone close with a deadly motive. This true-crime series tells stories of actual murders committed not by strangers but by someone the victim knew, someone hiding in plain sight, or someone leading a double life. These wolves in sheep's clothing use deception as a weapon to try to get away with murder.