Why do some people refuse to see the evidence when it exonerates a person who they feel victimized them or someone they care for?

In the wake of the Amanda Knox acquittal and the Casey Anthony trial, a lot of people scrutinize the evidence. The family of the slain young lady, in the Knox case, believe the prosecution had it right the 1st time. They do not want to believe the evidence is flawed, or could let Amanda off the hook.

There have been other cases here state side, where people have been set free by help of the Innocence Project. When the DNA proves, or made it highly improbable they killed the person, or raped the woman that earned them a conviction. When the victim was asked by reporters, what they thought, they didn’t care if none of the accused DNA was on them, in the room or inside them, they staunchly believe that man did it, in spite of what the evidence said.
Why do some flat out reject the evidence when it is overwhelmingly in the favor of the defendant? They can’t let go of their vengeance, they told themselves that was the person so long they can’t think any other way, something else?