Early one morning I came downstairs to the kitchen to make a cup of tea and noticed, through the French doors, evidence of a crime. On the garden lawn were the remains of a barbeque meal: paper plates, plastic forks and meat bones half hanging out of a bin liner. Convinced that the party held by our neighbour the previous night had got out of hand and someone had lobbed the rubbish bag over the fence, I gathered it up and lobbed it right back. Later that day I found the remains of a bird at the back of the garden and it occurred to me that a fox had dragged the bin bag from next door into our garden and set about devouring it, until distracted by fresher, juicier prey. The neighbours were innocent. This small incident showed me how easy it is to draw the wrong conclusion. Circumstantial evidence, bias against a suspect (the neighbours’ party had kept me awake), pressure for a quick solution or simply the desire for a neat ending can lead to error.
Was this the case in the murder of Mary Ashford? After she was found dead in a pit of water in Erdington in 1817 two men who worked at a nearby wire factory looked at footprints in the next-door field and blood drops on the nearby clover and came up with a theory of what had happened to her. They were convinced that the most obvious suspect, a local bricklayer, had murdered her. Members of the local gentry, one of them a magistrate, coordinated the investigation and were equally sure of their man. None of them had training in forensic investigation, which was, in any case, a barely embryonic discipline. Did they interpret the clues correctly? And if they were right, why was Abraham Thornton, the chief suspect, later acquitted, although not exonerated, at his trial?