Having spent six years as a murder squad detective in Bedfordshire during the mid-1970s and early 1980s, Trevor Marriott is no stranger to death.

Having spent six years as a murder squad detective in Bedfordshire during the mid-1970s and early 1980s, Trevor Marriott is no stranger to death.

“They were challenging murders because it was a case of doing, I guess, old-fashioned police work... way back then we never had the benefit of some of the modern investigative forensic methods open to people investigating these type of crimes nowadays,” he remembers.

“Some are more memorable than others and it was always emotional when you attend a crime scene, I think after a time you switch off and say ‘well, I have got a job to do’ otherwise your judgement gets clouded.”

The public speaker and author, who still works as a legal advisor for solicitors, is peering once again into the dark souls of 20 of the worst serial killers from around the world - many of whom may not be familiar to the many people fascinated by such crimes.

His two hour audio-visual show features more than 200 photographs of murderers, their victims and original crime scenes - many of which will never have been seen in public before - as well as video interviews with some of these killers. Much of the research comes from actual police records, newspaper articles, etc.

“Some of the documentaries made over the years on serial killers sometimes fall short of showing the pain and suffering the victims endured at the hands of these monsters and they also fall short of showing the pain and anguish relatives have had to suffer as a result of loved ones being murdered in an horrific fashion,” says Trevor.

“The show not only tells the story about the killers and their crimes but goes a long way to highlight those issues as well as the errors in judgement law enforcement has made over the years with some of these murderers.”

Those featured during the show span from the mid-1960s to the modern age, focusing on some now in prison or executed, some that have served their time and some that have yet to be caught.

“I’d been doing this show, the Top Ten World’s Worst Serial Killers. At the start I used to ask the audience ‘who do you think should be in the top 10’. Usually UK audiences come out with the likes of Fred West, Harold Shipman, Myra Hindley and Ian Brady... to be fair, with this show there are serial killers whose crimes far surpass the ones of those we’ve just mentioned. It’s going to be an eye-opener for audiences.”

It’s not for the squeamish or faint-hearted, he warns.

“At the start I highlight how serial killers are categorised, how they carry out their crimes, so right from the start the audience is fully aware of the type of serial killer they’re going to see because they’re not all the same. Their methods of killing, methods of trapping their victims are not all the same; in fact, some go totally against what leading experts on psychiatry and psychologists tell us makes a serial killer.

“Many of the photographs shown are of a very graphic nature, which some may find disturbing. It’ll be an interesting evening... lots of interviews with some of the serial killers themselves, clips of victims confronted by them in court... As likely as not, the audience may shed more than a tear or two before the evening ends.”

The World’s Worst Serial Killers comes to Chelmsford’s Cramphorn Theatre on February 6, Haverhill Arts Centre on April 24 and Basildon’s Towngate Theatre on June 18.