Paul Britton purported to have an insight into how killers think. He was at best deluded. Psychologists haven't merely enabled killers to remain uncaught but, through their 'expert' advice to parole boards, have also enabled known murderers to be released. Killers are relatively rare and in depth stides of them even more so. This means that there isn't a great deal of actual evidence for psychologists to test theories against and therefore conclusions drawn from them should only be accepted provisionally and never be applied to real life situations as though they were scientifically proven laws.
Detectives discounted his denial, which was convincing when you consider he had an incentive to say anything that might please his strange girlfriend. The point of the undercover exercise was not to extract a confession from Stagg, as no judge would have allowed a jury to hear evidence from a honey trap. Britton's pseudo-science aimed at securing more than a mere admission. He believed that his academic insights had given him the psychological profile of the killer.
Detectives set "Lizzie James" on Stagg to see if he matched Britton's description of a murderer, who was excited by his victim's fear and had a "deviant interest in buggery". When Britton ruled that the local loner did, the police believed him. Police say that Britton also told them that the murders of Rachel Nickell and Samantha and Jazmine Bissett were not the work of the same man, although Britton disputes this.
The specifics of Britton's folly are gruesome enough. As professor David Canter of Liverpool University said at the time, he barely mentioned the most striking and revolting aspect of the case: that the killer murdered Rachel Nickell in front of her child. As William Clegg, Stagg's QC, added at the trial, the transcripts of the conversations between his client and "Lizzie James" showed only that Stagg was a friendless man going along with a domineering but beautiful woman.
But dwelling in the detail misses the wider point. Just as dissenting economists are asking by what right their conventional colleagues demand to be taken seriously when no more than a handful warned of a coming banking crisis, so Parliament and the public should be wondering by what right psychologists demand a hearing.
It is not a reputable profession. The British Psychological Society dismissed all charges of misconduct against Britton in 2002, and no-one else has held him to account for what he did to Stagg and, indeed, to "Lizzie James", who went on to suffer a nervous breakdown.
It might not be true to dismiss the whole field as charlatanry, after all it is so wide ranging that what is true for part of the profession is not true for all of it, however there is clearly a tendency on the part of psychologists to pretend to have a more profound insight into the human mind than is the case. As the most media friendly branches of psychology are those that purport to offer shortcuts to solving big problems such as crimes or personal afflictions this means that most of the public faces of psychology are quacks and frauds.