Justice is rooted in “finding the truth”.
Generally we cannot be sure of the truth, but have to make do with what is “probable”. The ultimate aim is to find two overall best hypotheses : one is the “defense case”, the other the “prosecution case”. There may be alternatives within such hypotheses. We then have to assess the probability of each hypothesis, taking all the evidence into account. We may use slightly “gray” logic, where evidence may be said to render a hypothesis “unlikely, but still possible”.
Hypothesis formation is important. Sometimes the most difficult part of figuring the truth out is finding the correct hypothesis, and not overlooking some possibility.
We have to watch out for false assumptions or inferences. Such a
- All confessions are true
- Nobody is ever framed
- Documents are never forged
- There are no random coincidences
- Innocent people don’t lie
- Police officers never lie
- Police officers never plant evidence
- People are rational – that is they do things which help themselves, they are “motivated”.
- Experts never make mistakes.
Nevertheless, such assumptions/inferences are still normal when forming hypotheses to be tested and when evaluating hypotheses. We need to carefully consider especially whether actions are rational, and if they are not, whether the irrational “mistake” is reasonable or unreasonable, plausible or implausible.
If we call the prosecution hypothesis P and the defense hypothesis D, we will ultimately have one of the four possibilities below:
- P is possible and D is possible => Not guilty, although we are not sure.
- P is impossible and D is possible => Not guilty, we are sure.
- P is possible and D is impossible => Guilty, we are sure.
- P is impossible and D is impossible => Something is wrong. Either we missed a hypothesis, or made a false assumption/inference,
The rest of the article is examples to illustrate how this works, taken from cases I know well.
Examples of how hypothesis formation can be difficult
The difficulty of finding a correct hypothesis : this is difficult both for prosecutors and for innocent defendants. An example would be the Scott Peterson case when defense attorney Mark Geragos formulated a defense theory that was wrong, with regard to the time when Laci Peterson was abducted. He failed to take note of the time when Laci was seen walking the dog, and also the observations of the postman. It was also difficult to figure out the motive for why Laci might be abducted, or why someone would choose to frame Scott by planting the bodies near where he went fishing.
Often the process of forming a correct hypothesis is iterative, and the hypothesis has to be modified to take into account new evidence. Sometimes this may be difficult : for example, how should the apparent coincidence of a burglary in the Scott Peterson case be accounted for?
Examples of false assumptions / inferences
Point 1 : Numerous examples of false confessions exist. They are so common it is hardly necessary to give examples, but I will name Jeffrey Deskovic and Brendan Dassey.
Point 2 : Although cases where people are framed are not common, they do exist. Scott Peterson is such a case – the bodies of the two victims were planted in order to cast suspicion on Scott Peterson.
Point 3 : Edward Wayne Edwards forged numerous false documents, even going so far as to forge a fake birth date, five years later than his actual birth date.
Point 4 : Random coincidences do happen. For example Amanda Knox switched off her mobile phone on the evening that Meredith Kercher was murdered. It could be seen as suspicious, but there was a reasonable innocent explanation.
Point 5 : Innocent people do sometimes lie, sometimes because they think some circumstance ( such as an extra-marital affair ) will look bad, or because they are ashamed or think they may not be believed if they tell the truth ( Jodi Arias would be an example ).
Point 6 : Police officers do sometimes lie, an example would be the Debra Milke case.
Point 7 : Police officers do sometimes plant evidence, an example would be the Steven Avery case.
Point 8 : People sometimes act in an irrational way, especially when they are angry – perhaps because someone is not acting the way they want. An example would be Travis Alexander charging at Jodi Arias, even after she pointed a gun to keep him away. However if a hypothesis depends on a person acting in an irrational way, it’s likely wrong, especially if the irrational behaviour is over a long period of time.
Point 9 : “Junk science” ( experts making mistakes ) is very common. One example is the case of David Camm where experts testified blood spatter had to be from a gunshot when that was not the case.