The Power of the Cumulative Case
by Luke Nix
Last week I talked a bit about the issues with presenting evidence and arguments that do not lead to an exclusive conclusion and one way to obtain an exclusive conclusion. Many times a single argument cannot produce an exclusive conclusion. However, there is another way to eventually obtain that single conclusion.
Investigations take place all the time. People investigate different happenings and phenomena throughout the world. Investigations are how we come to understand and are able to explain things. In any investigation, a series of evidences are compiled. Any explanation that is to be considered plausible must account for all the evidence. Investigators attempt to enter an investigation without any assumptions prior to seeing evidence. The truth is that an investigator has a reason for investigating otherwise investigating would be of little value.
Many times an investigator has an idea that he wants to verify, or just see if it is correct. Other times, the investigator has no idea what happened, but something that he stumbled upon makes him want to learn more. It is quite important that an investigator recognize that (s)he is not objective and be willing to go where his acquired evidence is leading. For example, a crime scene investigator should not go to a crime scene already convinced that the crime was not a murder. This a priori (prior to evidence) conclusion may stifle the investigation (and conviction of a suspect) if the crime was, in fact, a murder. If the evidence points to a murder, and the investigator rejects that hypothesis, they may stall the investigation until some other explanation is available to him(her) to explain the evidence. This is not allowed in crime scene investigations because law enforcement has records upon records of cases that the current case may be compared to. If the evidence is similar, it is valid to rule the crime to be a murder. Then the search for a suspect may begin.
No single piece of evidence may be used to build a case or conclude the type of crime. Not very often does a single piece of evidence point to the possibility of only a single type of crime (see The Danger of Overstated Conclusions). When that is multiplied by the pieces of evidence, you end up with many possibilities of crimes for each piece. However, investigators look at all the different crimes that each piece of evidence points to and finds the common crime among the pieces of evidence.
This same process is used to determine suspects. In a court of law, the evidence is presented by the prosecution. However, they do not only present a single piece, since a single piece may point to other possibilities of crimes or suspects. The prosecutors present a “cumulative case” that consists of all the evidence. They also provide a scenario that consistently explains all the evidence…
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