Overview: They are marked by their ability to kill without passion and without remorse. Some are called psychopaths - a term that evokes nightmare images of murderers and monsters. But the label can also apply to men and women who are successful, intelligent, charismatic, charming and amusing - and so all the more dangerous. This week on the fifth estate, Linden MacIntyre looks at what makes a psychopath through the fifth estate's close encounters with of four of Canada's most frightening criminals.