Derek Broaddus and his family thought they were moving into their dream home — until a series of disturbing letters signed by "The Watcher" scared them out of it.

In addition to abusing and humiliating her daughters, Shelly Knotek would open her home to wayward friends and family in order to manipulate and torture them to death.

As a little boy, David Dahmer witnessed the birth of a monster right before his very eyes. Though he was raised in a seemingly normal house in 1970s Wisconsin, David watched in horror as his older brother's interest in dead animals and their bones, which he called "fiddlesticks," grew into a full-blown obsession. Even still, the boy had no idea that his older brother, Jeffrey Dahmer, would soon become one of the most notorious serial killers in history.

When the brothers' parents divorced in 1978, David moved out to live with his mother — just weeks before Jeffrey would butcher the first of his 17 victims. And when Jeffrey eventually went to trial for his disturbing crimes in January 1992, David changed his name and did everything he could to escape his family altogether. To this day, he's never given an interview and his whereabouts remain unknown. Learn more about David Dahmer and the chilling story of his upbringing alongside one of history's greatest monsters

"To think he could spend that whole evening doing all of the things they did and just having fun like a kid after murdering his family is preposterous."

Jeff Pelley was just 17 when he allegedly murdered his stepmom, his dad, and his two little sisters after being grounded on prom night for stealing CDs from a neighbor's house in 1989 — but did he really do it? Investigators settled on Pelley as their number one suspect when they learned that his father had grounded him for the burglary and forbidden him from attending prom without his supervision. Police also found the family's shotgun missing but no signs of a break in, suggesting that the murderer either entered from a bedroom or was otherwise close to the family. Though the initial case against Pelley was thin with no forensic evidence, murder weapon, or witnesses to hold him responsible, Pelley was nonetheless found guilty in a trial nearly two decades later and he remains behind bars to this day. So let's inside the maddening case of Jeff Pelley

"She had no idea, not a clue. I never had any blood on me or anything."

Just one year into his marriage to Sonia Sutcliffe, Peter Sutcliffe began his brutal killing spree as England's Yorkshire Ripper. Meanwhile, Sonia had no clue that while she was at home, her husband was raping and murdering prostitutes and other women with hammers and screwdrivers. By the time he was finally caught in 1981, he had slaughtered 13 women.

Learn the disturbing true story behind the woman who had no idea she was married to one of England's worst serial killers