Embedded hypotheses

When a murder case goes cold it can be for the simplest of reasons. Forensis recalls being hauled in to assist with a murder two decades old. He discovers that the original investigators have been barking up the wrong tree. Or branch.

Facts are curious things – we believe we use them to make sense of the world and each other. But John Updike wasn’t convinced; he considered them ‘generally over-esteemed for most practical purposes’. Another, much earlier writer, the irascible Hilaire Belloc, had a different concern about ‘facts’. In his 1912 poem The Microbe he scathingly wrote:

‘Oh! let us never, never doubt

What nobody is sure about!’

Updike tells us not to be too concerned about facts: Belloc warns us that facts can emerge from nothingness.

I am travelling with my colleague, an experienced senior investigating officer (SIO). We’re on our way to meet a forensic pathologist about a murder that remains unsolved, more than 20 years after it happened.

“What are you hoping to get from Dr. Walker?” I ask. “To explain parts of his report that I don’t understand and tell me anything he can remember about the case,” comes the reply.

The car drones around the M25 towards Gatwick airport. I look over the report. It describes the post-mortem and scene and in all the usual technical jargon. There’s no attempt to explain anything in a way that non-medical people might understand. That’s medics for you. Actually, that’s experts for you, guarding their territory with technobabble – a wall whose bricks are words.

I was in my second year at university when this murder happened. The young woman had died of extensive head injuries – bludgeoned to death, as the press like to say (or by blunt trauma as the professionals say).

The body was found in thick woods. There was a suspect but never enough evidence to prosecute

The body was found in thick woods. There was a main suspect at the time, although there was never enough evidence to prosecute him. He was still of interest.

“What was the weapon?” I ask.

“The photos are in my briefcase; I’ll show you them when we get on the plane.”

DNA has cleared up many unsolved cases, reaching back in time in a way that was previously unimaginable. A 29-year-old case in Wales was solved, when they exhumed the body of a man suspected of having raped and killed three girls in the 70s. DNA from the exhumed body matched that from the crime scene and connected him to all three victims.

But this is only half the story. The ‘Yorkshire Ripper’ investigation still casts a long shadow over today’s investigations. As the single most important case in the country at the time, the investigation was such a dog’s breakfast of incompetence and miscommunication that some women died because of its mismanagement. The report into these failings, carried out by Sir Lawrence Byford, was so sensitive that it was only published by the Home Office in 2006, 26 years after the trial, and only then in response to a Freedom of Information request. The truth is that a good many of today’s ‘cold’ cases are due to poor investigation, not a lack of technological wizardry such as DNA.

One of the canons of cold case reviews is to start again with fresh eyes. Don’t involve anyone who was involved in the old investigation. Go back and investigate the case again: go back to the original witnesses, the original exhibits and to the crime scene. Look through your own eyes, not the eyes and potential prejudices or failings of your predecessors.

As the plane tilts away from the Gatwick skyline, he hands me the photos. A thick, spiral-bound book, containing 5 x 7 inch colour images in a white card cover. Sometimes these cases are so old that the pictures are in black-and-white; they seem from a different world, if you were brought up in the age of colour. I look at the post-mortem photos first.

The ‘Yorkshire Ripper’ investigation was a dog’s breakfast of incompetence

As usual, they are horrific – a gallery of the muscle, fat, bone and internal organs, more reminiscent of a butcher’s shop than a systematic record of a clinical procedure. I’m only interested in the first few that show the body and injuries before dissection. I’ve had my fill of post-mortems and pictures of them. I close the book.

“And this is the weapon,” says the SIO.

He hands me the scene photos, open at a particular image.

“That’s not the weapon” I reply, as soon as I see the picture.

There are two ways of looking at these kinds of photos. Let’s call them the analytical and the holistic: horrible words, but bear with me. In the former, you pore over the image, trying to make sense of every detail, looking for things out of place, searching for clues, trying to make sense of it. In the latter, you apprehend the image in an instant, as a synthesis of objects in space and time, combined with knowledge of the case and your experience. Most cops use the analytical approach, particularly if they haven’t been to the scene.

“You don’t think it’s the…” The last word is inaudible, but I know what it is. He leans into me, trying to avoid being overheard. “You don’t think it’s the weapon?”

He’s surprised. Shocked even.

“Forget it, let’s leave it to the pathologist,” I say.

I quickly change the subject. I had broken one of my cardinal rules – never express an opinion until you have a rationale for it. The informality of the situation put me off guard. I should have kept my mouth shut.

Dr. Walker is in his 50s, an experienced pathologist who had dealt with many deaths. He has that slightly offhand, everything-is-routine manner – as if he’s seen it all before, which he probably has. Forensic pathologists are odd people. I’ve never been sure about the cause and effect here. Does the job make them odd (not just death, we all die in the end) but violent, sudden and horribly unfair death? Or are they just odd individuals to start with?

There is something about medicine that inculcates bombast and arrogance

And of course, there is something about medicine, or the fringes of medicine where forensic pathology lies, and its culture, that inculcates bombast and arrogance. Neither of these characteristics is useful in an investigation or a court room. Is this why so many of them fall on their own swords in the end?

We work our way through the report, to check our understanding of his findings, conclusions and thinking.

“Have you got the pm [post-mortem] and scene photos?” asks Walker. The SIO hands him the pm photos. He works his way through the book, comparing the images with what is in his report. It doesn’t look as if he is going to change anything.

“This is what we think the weapon is,” says the SIO, handing the other book to Walker.

The photo shows a thick, heavy, branch, about four feet long, with areas of blood-staining on it.

“That’s not the weapon,” says Walker. “Did you see her injuries? She looks as if she had been hit by a car. This doesn’t have the mass to cause such serious injuries.”

And there’s my missing rationale – the branch isn’t big or heavy enough. I stay quiet.


More than 20 years had passed since that murder. Until this point everyone believed this branch was the weapon. This is not the only occasion I have come across this phenomenon, which I have heard referred to as an ‘embedded hypothesis’. Nor is it the worst example I have encountered. An idea creeps into the minds of the investigation team, by a process so slow that it’s unnoticeable. It’s a sort of cognitive fossilisation, from which a ‘fact’ emerges. What was unknown becomes ‘known’: Belloc was right.

Some months later, the suspect, now an octogenarian, stood trial for the murder. He was acquitted.

I still don’t know what the actual weapon was.

Forensis – our resident forensic expert – has been involved with criminal justice in the UK for around four decades and contributed to thousands of cases, from investigating crime scenes to giving evidence in court.