Two years before he embarked on a killing spree in Buffalo and New York City, Joseph G. Christopher’s friends and family noticed a seismic shift in his personality. The 23-year-old was beset by mood swings and paranoia. His hold on reality was unraveling. In the end, it would prove fatal.

Thanks to an unsuspecting benefactor, Duncan gets a fresh start in North Dakota. But his blog entries begin leaving chilling clues as to what lies ahead. In 2005, his violent impulses lead him to Coeur d’Alene, Idaho and his worst crime yet.

A teenage sex offender carried out horrific crimes against young boys in Washington in the late 1970s before being sent to a treatment program, followed by prison. Fourteen years later, Joseph Edward Duncan III was paroled, free to carry out a murder spree that claimed the lives of three kids.

In the 1970s, after abusing his children and getting away with it, Joseph Kallinger enlists his son in a mission from God that terrorizes the suburbs of Pennsylvania and New Jersey.

The adopted son of cobblers began having hallucinations as early as 15 years old. They were harmless at first — but tragically, they wouldn’t stay that way.

After years of charming women into getting engaged to him, Henri Désiré Landru had perfected his system of making his fiances, and all of their wealth, disappear.

In France, a con man charmed women into getting engaged before robbing them and taking them to his country villa. Where they all mysteriously disappeared.

Numerous childhood traumas led Tsutomu Miyazaki to create a monstrous character in his head named "Rat Man" that eventually took control of his thoughts and actions.

In 2010 a serial killer terrorized an area of Philadelphia known as the Badlands. Police swabbed hundreds of men for DNA before a CODIS backlog revealed they’d had what they needed all along.

Mack Ray Edwards was proud of his career as a heavy machine operator. It made him important on construction sites. But the very same machine he used to build a series of freeways in Los Angeles would also be used to hide the bodies of his murder victims.

When Veronica Compton met Kenneth Bianchi, she was working on a play about serial killers. She interviewed the “Hillside Strangler” as part of her process. But then he charmed his way from research subject to love interest, and Veronica found herself wrapped up in a horrifying scheme.

Wesley Shermantine and Loren Herzog went from hunting animals to preying on humans. Even as they grew older and settled down, they continued their spree.

Wesley Shermantine and Loren Herzog grew up in the California countryside, hunting for deer and elk. In high school, they turned to methamphetamine to recreate the thrill they once got from hunting. But as their drug use intensified, they needed something stronger to maintain their high. They needed to kill, and this time, their prey was human.

At a young age, Mikhail Popkov developed a deeply misogynistic view of the world. As an adult, he used his power as a police officer to act on these feelings, murdering women he deemed to be morally defunct.

Police had taken Roger Kibbe into custody numerous times but never had enough evidence to arrest him. Each time he was let go, he went on to claim more victims. But a discovery by a forensics investigator was exactly what authorities needed to put him away for good.

After killing his first victim, Roger Kibbe decided to keep a low profile. But years later, his urge to kill returned. By mid-July of 1986, he had killed four young women — three of them in the past three months. And he had no intention of quitting.

Roger Kibbe spent most of his adolescence filled with rage. And while he had a long list of arrests by his mid-30s, it was never for violent crimes. Until one day in 1977, he finally snapped.

In 1946, the mysterious Phantom Killer who had terrorized the town of Texarkana for months disappeared just as quickly as he'd appeared.

In 1946, the city of Texarkana was plagued by a series of attacks and murders on couples parked in their cars. Police, however, failed to act quickly enough, potentially giving the murderer enough time to get away.

As a child in the ‘80s, Matthew Macon was thrust into a world of chaos and turmoil. From a young age, he was in and out of federal institutions, but nothing seemed to curb his darker impulses. Eventually, he gave into them, and his killing spree began.

Viktor Sayenko and Igor Suprunyuk were insecure children, scared of the world around them. As teenagers in the 2000s, they pushed themselves to move past their fears. But in the process, they unlocked something even more terrifying: an uncontrollable desire to kill anything and anyone.

Glennon Engleman had claimed two lives during his insurance fraud schemes and escaped police detection with ease.