After giving a talk about the crimes of West, Bellfield and US serial killer Ted Bundy, Mr Wansell was asked whether there were any multiple murderers on the loose in Britain today.
"I'm not going to take that question lightly. There are at least two, maybe three. There are a whole series of unsolved murders that could be linked. I would say there are at least three serial killers out there," Mr. Wansell told an audience of around 300 people at Dingwalls in Camden, north London on Tuesday, 26 March.
He was then asked if it was harder to serial killers to get away with their crimes in the era of CCTV and social media.
Has DNA Made it Harder for Serial Killers?
"DNA and forensic science has changed the nature of where we are. But just as we have become more sophisticated, so have serial killers. They might now use latex gloves and know that they must not leave any fibres. They watch CSI just as we do. They have the capacity just as we do," Mr Wansell said.
He was then asked if he thought serial killers could feel guilt or be rehabilitated into society and his answer was brutally simple.
"They don't feel guilt and I don't think they can be rehabilitated," Mr Wansell replied.
He also repeated a comment which serial killer Ted Bundy had said shortly before he was executed on the electric chair in Florida in 1989.
"Guilt doesn't solve anything and I don't really need it," said Bundy, who killed more than a dozen women in the states of Washington, Utah and Colorado.
He escaped from jail and fled to Tallahassee, Florida, where he killed two university students in the infamous Chi Omega sorority house murders and then 12-year-old Kimberley Leach.
Bundy was finally caught, prosecuted and sentenced to die but spent a decade on Death Row.
Mr Wansell said Bundy — who is played by Zac Effron in a movie out later this year — was "charismatic, attractive" and fiendishly intelligent but was also a "monster" who had sex with his victims after they were dead.
"One of his tropes was that he'd go back to the bodies, shampoo their hair and apply make-up. He had a sort of relationship with them. It sounds utterly bizarre but it wasn't bizarre to Theodore Robert Bundy. It was his way of maintaining control over their bodies," Mr Wansell said.
In 1995 Mr Wansell was chosen by the Official Solicitor to write an authorised book about British serial killer Fred West, based on police tapes, documents and West's own prison autobiography which he left behind when he hanged himself in Birmingham's Winson Green prison.
The book, An Evil Love, was published in 1996 and in 2011 he wrote another book, The Bus Stop Killer about another UK serial killer, Levi Bellfield, who is currently serving two whole life prison sentences for murdering women in south west London.
Are Serial Killers Born or Made?
Mr Wansell was asked if he believed in "nurture or nature" when it came to serial killers.
"I don't think there is an evil gene. There have been masses of arguments about it. I think there is a predisposition. It's one on top of the other. You are not born a devil," Mr Wansell said.
He was also asked why serial killers were usually men.
Mr Wansell said there were a few female serial killers — Aileen Wuornos in the US and Joanna Dennehy in the UK — but they were in the minority.
"It's usually men because a lot of serial killers are sexually motivated. There are few women that have that same drive. Sex is about control, not penetration. There is something in the male character which has the desire to control the woman," Mr Wansell said.
Podcast Started From Nothing Now Has 120,000 Listeners
The evening was put on by Adam Lloyd, the host of the UK True Crime podcast, which has around 120,000 listeners and is growing all the time.
"My background is in HR so I knew nothing about podcasting. But I thought I'd go for it. Some of the reviews I have got have been pretty bad. One guy said he would rather listen to two cats fighting in an alley," Mr Lloyd said.
"Why has it been successful? Because I'm just being me. I mention the mighty Leeds United and stuff I don't like, like the Kings of Leon, and I'm authentic. It's also about consistency. It always come out on Tuesday mornings. It's also about the quality of the audio and of course about the research," Mr Lloyd said.
Each episode is focused on a different true crime in the UK.
This week's episode focuses on the murder of Joan Roddam, 74, at her home in Cornwall in 2003.