Between 1975 and 1980, terror gripped the northwest of England. A serial killer, who with little imagination the newspapers christened “The Yorkshire Ripper,” identified women alone on the streets in the evening, some of them prostitutes, and convinced (or forced) them into his car. The predator, armed with a hammer and screwdriver, killed thirteen women and injured at least seven others. Although he seemed untouchable—almost a ghost that reminds the public of the mysterious Victorian serial killer Jack the Ripper—the police had many opportunities to arrest him. Nine times, in fact, investigators questioned Peter Sutcliffe, a truck driver who for one reason or another continued to pop up on the list of possible suspects but ended up being released each time.

On one occasion, the police showed Sutcliffe a photograph of a boot print found next to a victim, but no one noticed that the man was wearing exactly the same type of boots at that moment. On a different occasion, a £5 note was found in the pocket of a victim. From the serial number, it was traced back to the transport company Clark Transport, where Sutcliffe worked. But still no one made the connection. Sutcliffe had been arrested in 1969, because he was found armed with a hammer in a red light district. And a friend of his, Trevor Birdsall, had accused him in an anonymous letter of being the serial killer everyone was looking for. Tracy Browne, only fourteen years old, who survived five blows from the killer’s hammer, described his appearance so well that the identikit obtained looks like a photograph of Peter Sutcliffe. Descriptions from his other victims were similarly close.

But none of this was of any use. Eventually, Sutcliffe ended up in jail by accident, on January 2, 1981. Traffic police stopped the car in which he had secluded himself with a prostitute. They were both taken to the station, and it turned out that the car was stolen. It was the same type of car seen several times near the crimes. The man explained that he changed the license plate on the car so as not to let his wife know that he was visiting prostitutes. Incredibly, the police believed him and once again were about to release him, when a car check led to the discovery of a screwdriver. Not far from where Sutcliffe was stopped, a hammer and a knife were also found. Only then, under pressure, did Peter Sutcliffe confess that he was the Yorkshire Ripper.

But why wasn’t he arrested earlier? Why was he always excluded whenever he was suspected or questioned? Because he didn’t fit with the investigators’ idea of ​​the killer. The police, for example, had received a tape in an anonymous package in which the alleged killer bragged about his successes. His voice had a strong northeast accent, which Sutcliffe did not possess. But that tape was a fake, the joke of a mythomaniac. There were many reasons to suspect that fact, yet what the voice said in the tape fit in well with the idea the police had built about the “killer of prostitutes.” Besides, Sutcliffe was married, and he had said he didn’t hang out with prostitutes. This, in fact, was the real problem: investigators were convinced that, just like Jack the Ripper, the killer “only killed prostitutes.” “He’s a man who hates prostitutes,” the detectives had declared on TV. And from this certainty all the rest descended.

They were, however, totally wrong.

Sutcliffe was a misogynist, a man who hated all women. In fact, although he had hit some prostitutes, they were not his only victims. He was simply looking for single women, and in some areas, at night, it might be easier to find a prostitute. But they were not the only ones he killed. When a woman who did not prostitute herself was murdered by Sutcliffe, there were a thousand pretexts to identify her as a “naughty girl.” Maybe she had economic problems and therefore, the detectives speculated, she had to prostitute herself to get by, even if there was no evidence that she ever did.

But when women or girls had been attacked by Sutcliffe, and miraculously managed to escape, their stories—the details they gave, the precise descriptions they offered of the assailant—were simply ignored, because these women did not seem the type of victims of the “real” Ripper. The police were looking for Jack the Ripper, an evil menace, not some petty Bradford truck driver.

So we have to ask ourselves: Why did the police fail so miserably? Because the investigators let themselves be blinded by their prejudices. And most importantly, they refused to change their minds whenever the evidence disproved their beliefs. It was a bad case of confirmation bias, yes, but they were not the only ones suffering from it.

“We all have blind spots in our knowledge and opinions,” writes psychologist Adam Grant in his excellent book Think Again, devoted to questioning one’s own beliefs. “The bad news is that they can leave us blind to our blindness, which gives us false confidence in our judgment and prevents us from rethinking. The good news is that with the right kind of confidence, we can learn to see ourselves more clearly and update our views” (Grant 2021).

The British investigators in the Yorkshire Ripper case could have taken the same hint by listening to what almost a century earlier another English detective, however imaginary, had said: “It is a huge mistake to theorize before having the data in hand,” declared Sherlock Holmes in the short story A Scandal in Bohemia. “Gradually we begin to distort the facts to make them agree with the theories, rather than formulating theories based on facts.”

And this is a trap in which everyone, to some degree, can fall into. Why? Because we are not accustomed to thinking like scientists, and so we are always more likely to seek confirmations for something we believe in rather than facts that could disprove it.

Reference

Grant, A. 2021. Think Again. New York, NY: Penguin Random House, 35.