He could be your neighbour, he might be your gardener, he could be hunting prostitutes, drifters, hitchhikers, old widows or young boys. He could strike at any time, and in any place, and with horrifying regularity, he does. According to an FBI Behavioural Unit study, serial killing has climbed to an almost epidemic proportion. In the UK there are up to four unidentified predators with many more travelling around continental Europe. Authorities estimate that there are between 35 and 50 serial killers on the loose in the USA - and new reports of suspected killers are constantly surfacing all over the globe. This is a look at serial killers at large, from one of the world's foremost authorities.