More than grid verses organic street plans there is also the ease of travel, major roads, parks, back alleys, rail etc. Then you get into road works, strikes and so on.
Given that serial killers target at random though the killer is freed up from any consideration of the habits of his victims and perhaps it is only his own needs to get safe, not be detected and ease of travel that may give clues to his whereabouts.
So your friend, with his more sophisticated approach may be on to something.
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It's hardly likely that any definitive outcome would be recognised. That would be something for posterity to sort out.
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