In 2007, a young policewoman was killed in Germany.
Someone climbed into her police car and shot her in the back.
Luckily, they found the perpetrator’s DNA on the seat.
Then, checking the files, they found the same DNA on crimes going back to 1993.
The first was an old lady, strangled with wire in her own house.
Then the same suspect murdered an old man.
The perpetrator’s DNA was female, most likely Eastern European.
It turned up next on a syringe found by a child.
And over the next four years in 20 car thefts.
Putting the clues together, the police were looking for a female Eastern European immigrant, probably a homeless drug addict by the evidence.
They took DNA from 3,000 women who fitted that profile.
But none of the results matched the sample.
The police caught some of the criminals involved but they all denied this woman was an accomplice.
Günter Horn, the prosecutor in charge, wasn’t surprised by that.
He knew they must be terrified of this mastermind.
He said: "She leaves no fingerprints, so she wears gloves. She is never seen, there are no witnesses. She just does the job and disappears."
Her DNA was found on six murders and at 40 crime scenes over 15 years.
It was found on a bullet, on a teacup, a biscuit, a windowsill, a rock used to break a window – even on a toy gun.
The newspapers called her "The Phantom of Heilbronn" and "The Woman Without a Face".
She was the criminal mastermind who evaded all efforts to catch her.
In a separate incident, the charred corpse of a man was found.
To discover his identity, the police took a swab of his DNA.
But the DNA showed the corpse to be an Eastern European woman.
That was obviously wrong.
So they took another sample with a different swab.
And this time the DNA correctly showed it to be a man.
This led the police to test the swabs they’d been using to collect the DNA at the crime scenes.
They found all the swabs had been contaminated at the factory where they were made.
The factory where they were all made by Eastern European women.
So the DNA they’d been collecting for 15 years wasn’t from a criminal mastermind at all.
It was the DNA from one of the women who made the swabs.
Every time they took a sample, it was her DNA on the swab.
The Eastern European woman at the factory that made it.
And for 15 years, the police had been searching for a criminal mastermind who didn’t exist.
All because nobody questioned the infallibility of scientific process.
Stefan King of the Berlin Association of Lawyers said: "We tend to be so blinded by the shiny, seemingly perfect evidence of DNA that we ignore the bigger picture."
Which, of course, is what people everywhere do.
In every business, especially ours.
Once a seemingly scientific hypothesis has been developed, it is beyond question.
Because we all believe what we’ve been taught at university.
Which is that only stupid people question the infallibility of quasi-scientific thinking.
(Dave Trott is the author of Creative Mischief, Predatory Thinking and One Plus One Equals Three. This article first appeared on CampaignLive.co.uk)