Peter Tillers discusses why DNA can never be regarded, on its own, as conclusive evidence of guilt or innocence. 

This post makes me wonder about the possibility of a kind of schematic argument map showing how the argument from say a DNA match to guilt would have to go in some more-or-less general version.  This map would display the numerous inferential steps, assumptions etc. – i.e., the numerous points at which the inference might fail.

John Burns, who at the time was quite senior in the Hong Kong police and had experience in training detectives, proposed this kind of idea in masters dissertation.  He called them “pre-structured argument maps”.  You would have such a map for each typical situation in which a detective might be trying to make the case for guilt, e.g., one for shoplifting.  The pre-structured map would embody (a) a good understanding of the overall structure of the case that would have to be made out, and (b) the accumulated wisdom of experienced detectives as to all the bases that need to covered – e.g., the detective would have to have evidence to rebut the defendant’s claim that he already owned the item. 

Then, rather than piecing together a case (whether in argument map form, or more traditional format) from scratch, the detective would check off the various aspects of the case on the pre-structured map, removing parts which are inapplicable to the particular situation, etc.. Along the way the detective would be learning what a good case looks like, being exposed to the myriad ways in which the case might be defeated by a clever lawyer, etc.

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