Defined by the FBI as individuals who commit at least three separate murders over time, with cooling-off periods between each event. These cases reveal patterns of control, compulsion, and psychological escalation — distinct from spree or mass killings, which unfold in bursts or single locations.
Hallie Ann Seaman: A Murder Unsolved for Nearly Fifty Years and the DNA That Revealed Her Killer
In 1975, 25-year-old architecture student Hallie Ann Seaman disappeared after leaving her university studio in Seattle. The following day, her burned-out car and body were found miles apart. For nearly fifty years, her killer remained unidentified — until a DNA match revealed a name that had never appeared on the original list of suspects.
Read MoreRomulus Vereș: The Satanic Delusions Behind the Man with the Hammer
Between 1972 and 1974, a series of brutal attacks terrorised the Romanian city of Cluj. The perpetrator became known as the Man with the Hammer, but when investigators finally identified Romulus Vereș, they encountered a bizarre explanation. He insisted he wasn't responsible for the murders, claiming that satanic forces had stolen his appearance and committed the crimes in his name.
Read MoreChristine Falling: The Babysitter from Hell
In early 1980s Florida, a series of children became seriously ill or died while in the care of teenage babysitter Christine Falling. For more than two years, each case appeared to have its own explanation, until investigators began to see a disturbing connection.
Read MoreCary Stayner: Monster in Yosemite
In 1999, a series of murders shattered the apparent safety of Yosemite and left investigators searching for a killer. Living nearby was Cary Stayner, a quiet handyman who had spent years exploring the park and searching its forests for Bigfoot. Soon, Yosemite would become known for a monster of a very different kind.
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