So, what might we do -- as in what cognitive strategies should we employ -- to prevent falling into such a trap?
Well, being aware of this issue would be an obvious thing. A lot of dealing with cognitive biases is simply being aware that they exist. And if one has any belief that is at all controversial it helps to ask every so often "why do I actually believe this?" This is especially the case as new evidence emerges or experts change their opinions.
I'm not sure we can do a very good job at avoiding this sort of trap. The level of rationality required is extremely high. Being a less vengeful person in general might help. Maybe there's some good that comes out of this. If one is ever in a similar situation just think about the Kerchers and realize that one is likely not in a circumstance to judge things well.
See: You Be the Jury, The Amanda Knox Test
While we hear about Bayes' Theorem being under threat in some courts, it is nice to savor the occasional moment of rationality prevailing in the justice system, and of mistakes being corrected.
Congratulations to the Italian court system for successfully saying "Oops!"
Things go wrong in this world quite a bit, as we know. Sometimes it's appropriate to just say "hooray!" when they go right.
Discuss, or celebrate.