Joe and Shawndrea follow up on a handful of Phoenix sightings since her disappearance and begin to question whether she'd been lured into a new life more dangerous than she could have anticipated; a surprising lead goes to an unexpected locale.

Phoenix Coldon vanishes; investigative reporter, Shawndrea Thomas, and retired deputy Police Chief Joe Delia attempt to unravel the mysterious unsolved case in the hope of finding justice for Phoenix.

"Mark of a Killer" examines the disturbing behaviors of serial killers. Step into the minds of some of the worst serial killers to date as they taunt law enforcement. Some of these killers get a perverse gratification by habitually stealing mementos from murder scenes including things like shoes, jewelry, keys, and even body parts. All of these stolen clues are meant to taunt the investigators while they build up their notoriety -- these killers often lead trademark clues behind as a way to mark something that was theirs but ultimately is their downfall as investigators use these as clues.

For more than 25 years, "Dateline" has brought viewers investigations into some of biggest mysteries in America. This entry in the franchise takes a second look at some of the most mysterious cases of recent history. Hosted by Emmy-winning journalist Craig Melvin, the show explores the stories through firsthand accounts told by people who are close to the crime, including investigators who dedicated their time to the cases and family members who are still trying to confront the tragedies that befell their loved ones.

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?

Some lies are so life-changing that people are willing to kill to keep the truth from getting out; through twists and turns, investigators dissect how each complex lie turned into a horrific tragedy.

"Murder for Hire" gives an exclusive look into the dark world of contract killings, showcasing some of the most fascinating murder for hire cases ever caught on tape. In an alarming trend, investigators are seeing a sharp increase in hired hits across the country, and those attempting shockingly include: housewives, wealthy bankers, military officers and even grandmothers. From scorned lovers to jealous relatives, the show explores in rare, never-before-seen footage, how a seemingly good relationship can go wrong and the emotions surrounding the reveal when an intended victim discovers a hit has been taken on their life. Each standalone episode features a different case of undercover agents immersing viewers into the real-life sting and investigation as they attempt to catch the perpetrator and ultimately prevent a murder.

In this eight-episode series, viewers hear directly from detectives who investigated cases that haunt them to this day. These true-crime stories -- from mysterious vanishings to twisted family murders -- are the "unforgettable cases that disrupt law and order, and keep authorities up at night," says Investigation Discovery.

"Killer Couples" is in the same vein of the long-running true-crime series "Snapped," which tells stories of people who commit murder or attempt murder, but with a focus on 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.

Think "Cold Case" meets "CSI" with a bit of "Rizzoli & Isles" mixed in, then make it real. That's the formula for this unscripted procedural drama that follows two veteran female investigators as they attempt to crack murder cases that have lingered for years without answers and closure. Kelly Siegler is an attorney and former Texas prosecutor who successfully tried 68 murder cases in her 21 years on the job, including 20 capital murder death penalty cases in which she secured the death penalty in 19 of those trials. She gets help from veteran detectives, who dig into small-town murder cases that have gone unsolved for years in the hope of getting justice for the victims and their loved ones.

A vibrant young woman is found dead, hanging naked, bound and gagged, in the courtyard of her billionaire boyfriend's Coronado, Calif., mansion, just two days after his 6-year-old son suffered a shocking accident. The sheriff rules her death a suicide, claiming she was distraught over the young boy's grim prognosis, but after seven years of endless public intrigue and speculation, a wrongful death suit holds someone accountable. In the wake of the civil verdict, Prosecutor Loni Coombs, crime journalist Billy Jensen, and forensic criminologist Paul Holes embark on a fresh look at the case. Meeting with experts, family members, witnesses, and never-before-interviewed law enforcement officials, they create a case file with compelling new evidence and present it to the San Diego Sheriff's Office for review.

Examining the disappearance of Crystal Rogers from her small Kentucky town and the mysterious death of her father a year later; as investigators look closer, other unsolved cases emerge.