I often hear people say they want evidence-based decision-making, but they then behave in a totally different way. My view is evidence is all observed facts relating to the issue at hand. Only too many people think evidence is that which supports their hypothesis, and that which does not is irrelevant. Thus collecting evidence requires dispassionate thoroughness, while determining what such evidence means requires clear logic. However, not everyone is capable of being truly dispassionate once they have reached a conclusion; they do not like revisiting previous decisions.
Consider the hypothetical statement, John murdered Joe. Joe’s apartment door was open, whereupon another apartment dweller found the body, which had a bullet through his head. Forensics tell you he died of the bullet wound at about 1 am. Joe is dead, which meets the first criterion, and there is no gun left behind. So, was he murdered?
Superficially, suicide can be eliminated, but in principle someone else could have removed the gun, so there are actually two hypotheses consistent with that evidence. The police could test the victim’s hands for gunpowder residue, but suppose they jump to a conclusion and don’t bother? Some innocent could go to jail.
So, what about John? People state that earlier John had a heated argument with Joe in his apartment. John has no alibi; he states he was in bed asleep at the time. They find John’s DNA in the apartment, but apart from Joe’s, nobody else’s. After a lot of questioning, the police find someone who saw a man walking away from the apartment block “early in the morning”. The person looked like John and was wearing a hoodie. John owns a hoodie.
So, what do we have? Strictly speaking, nothing against John. John does not deny the heated argument, and it also explains why his DNA is in the apartment. That no other DNA is there is not necessarily indicative that nobody else was there, but merely that nobody else left enough to be found. Just because you argue does not mean you will murder the other person, and anyone that lives alone is likely to be in bed asleep at 1 am. As for the “identification”, all we have is a man of about John’s height was wearing a hoodie. Such evidence can be consistent with a statement, but it can only prove the statement if it falsifies every other possibility.
Now, a real case. A young couple were at a New Year party near a marina and also present (and relevant to this) were our accused, who was drunk and behaving badly by trying to chat up any female, and a “scruffy man”, who was never identified and was alleged by the police to be the accused. The “evidence” in support of this was somehow they got a scruffy photo of the accused and one person picked this photo out of a photo lineup. He was later to say that the photo indicated the degree of scruffiness but it was not intended as a full identification, and as it happened, this photo did not look particularly like the accused. The two young people were ferried out to a boat at the invitation of scruffy man. The man who ferried them out described the boat as a forty-foot ketch. The couple were never seen again.
The police arrested the accused, and claimed they had been taken to his boat, a twenty-six foot sloop. The accused had been repainting his boat, and the police claimed he was covering up evidence. The accused claimed it was normal maintenance. The witnesses claimed that the water taxi ferrying the victims out left on a given course and gave a time for how long it took to get there. That would put it a minimum of ninety meters away from the sloop. The police maintained there was no ketch, but independently some claimed to have seen it, and their location of it was roughly where this water taxi went. In evidence there was no ketch, the police produced a montage of the whole area, and there was no ketch. The problem then was the various photos were all taken at different times, and all of them well before the party. The police argued the two were locked away in a cabin of the sloop, and there were scratch marks where they had fought to get out. Evidence was that the scratch marks had been there before. Finally, after some time, forensics found two hairs belonging to one of the victims on a blanket taken from the sloop. What do you make of that?
If someone were making deep scratches trying to get out (a futile gesture but that is beside the point) there would be a lot of other DNA there. Ha, the police said, the accused cleaned that up. But if he was good enough to clean up all the DNA from everywhere else, why not get rid of the bedding, because it was almost certain that something would be left behind? In my opinion, the key evidence was where these victims were taken. If you know anything about boats, you know the difference between a sloop and a ketch (one and two masts is one major difference) and the ferryman was a master mariner. Further, if the people who saw the water taxi go out and come back have it going to a different place than the sloop, coupled with the ketch, the police have the wrong boat.
However, the accused was found guilty. Part of the problem was the defence lawyer. Thus when the police asked one witness did you not pick photo C from a photo lineup, the witness had to agree he had. He was later to say that had the defence lawyer asked him was the scruffy man he had seen now in the court, he would have answered no. But the lawyer had no idea what the witness would say, and he relied on his oratory at the end. The trouble was, his oratory was not up to scratch, and he had failed to establish sufficient facts. On the basis that the accused gets the benefit of reasonable doubt, I believe this was a miscarriage of justice, but thanks again to lawyers, his appeals process has run out. Had I been on a jury I would never have convicted, not because I am sure he was not guilty, but because I am sure there is reasonable doubt. However, the emotion of these two young people presumably being killed, together with angry parents, meant the jury almost certainly did not view this dispassionately. Evidence will be consistent with the truth, but it can also lead many down a completely different path.