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Juries can only consider evidence prsented to them in court. In all these instances, the prosecutors filtered the evidence very heavily to obtain the (predetermined, IMO) results they and their masters wanted.
Read the transcripts of the McVeigh trial, for instance. Of the nearly two dozen eyewitnesses who saw McVeigh in OKC, none (zero, zip, nada) of them were allowed to testify.
Why? Because all of those witnesses had testified (deposed) that McVeigh had someone else with him!
Um, McVeigh had a defense attorney, right? Isn't it his job to call those people? Did he not know about them? If not, was he that stupid?