For a juror, the psychological conflict is palpable. In one sense, they are following an emotional narrative featuring a victim, a villain, and a cast of supporting characters--some good, some bad, most somewhere in between. The trial is a story told from different perspectives, and the jury is the audience taking it all in from front row seats. 

In another sense, jurors are being asked to make a logical decision detached from emotion. Someone's life is hanging in the balance.  If they don't get this right then either the victim won't receive justice, or an innocent person will be convicted. 

What the last three decades of cognitive science research tells us is that we are not capable of making decisions detached from emotion. The two positions described above are not mutually exclusive; they overlap to a significant degree.  Both the dramatic narrative and the impact of clinical facts feed into the thinking of every juror.  And since our brain isn't structured as a series of insulated silos--some for facts and others for emotional reactions--the final decision will be pulled from the murky stew that includes both.

Another way to say that is, "reason" and "emotion" are categories we use to simplify communication, but they don't tell us anything about how our brains really work.  And the truth is that the messiness and imprecision of the human brain can't be contained by the law, or any other social construct, no matter how demanding or threatening. Attorneys can stand in front of the jury and repeatedly remind them that they must make a decision on "the facts" and not be influenced by "emotion," but they may as well be telling jurors to hold their breath while deliberating.

In the end, the jurors in this case will make carefully considered decisions. They will try their best to keep the evidence in front of them, and be guided by the court's admonition to render a verdict solely on the veracity of that evidence.

But we know from watching the trial that they have seen contradictory evidence. They have listened to credentialed experts give different opinions on the same evidence.  They've been faced with the best information both sides of the case could find to persuasively put in front of them.  What's true and what's false?  Whose opinion matters most?  Whose testimony is reliable enough to guide a decision? 

None of this is clear. None of the "facts" of the case cut through the ambiguity and point to an unassailable decision.  The decision will instead be made with emotion weighing heavily on every comparison of evidence.  It simply can't happen any other way--at least not while humans are the decision makers.