Mark Hobson walked out on his happy family with no explanation on New Year's Day. Five years later he went on a murder spree, killing his girlfriend, her sister and an elderly couple. Criminologists and psychologists try to decode this enigma.

A look at the 21-year-old killer who brutally took the life of British student Matthew Pyke, after developing an obsessive infatuation with his girlfriend.

He decided to become a serial killer and brutally snatched away the lives of five innocent men. This is the story of the calculated murderer.

A look at the convicted double-murderer responsible for taking the lives of Becky Godden-Edwards in 2007 and Sian O’Callaghan in 2011.

A look at the welsh serial killer known to some as The Wildman, who got four life sentences for a string of gruesome murders and sexual assaults.

A look at the brutal murderer, dubbed The Beast of Manchester, who claimed the lives of three teenage girls in the 70's.

A chilling look at a man responsible for one of the biggest police investigations in Bristol - the cold-blooded murder of Joanna Yeates.

A look at the Scottish serial killer who preyed on young girls between the ages of five and 11 throughout a six-year killing spree.

A profile of the man responsible for the cold-blooded murder of two teenage girls in 1977, known as the World's End Murders.

After killing 12 people in Cumbria in one of the worst firearm crimes in British history, Derrick Bird turned the gun on himself. Criminologists and psychologists explore what could have made Derrick, known as popular and funny, snap so dramatically.