I don’t know if the rules were different 60 years ago and I’m not a legal expert but isn’t the whole idea of having a jury of your peers (as opposed to professional jurors) to consider everything they heard in the trial and question it if in their own judgement they think something was incomplete or wrong? I do know that today the judge tells jurors not to do their own research so going out on the street and finding the same knife would probably result in a mistrial.