You can read the actual OIG Report [1] it is online, but the interesting bit is here, in Chapter 7 (page 269):
"Based on our investigation, we concluded that the three FBI examiners who misidentified Mayfield's print were confused by the fact that the fingerprint on the Madrid bag contained as many as 10 points that corresponded to details in Mayfield's known finterprints in relative location, orientation, and intervening ridge count. This degree of similarity is extraordinarily rare and confused three FBI fingerprint examiners as well as a fourth, outside, court appointed examiner."
I don't know how much you know about fingerprint forensics, I just know what I read, but a 10 point match is considered pretty strong from what I've read. And as I mentioned earlier, its a statistical thing not an exact thing.
"Despite finding that Mayfield’s print was not an identical match to the print left on the bag of detonators, FBI fingerprint examiners rationalized away the differences, according to a report by the Department of Justice’s Office of the Inspector General (OIG)."
It seems they need to totally separate the finger print examiner from the investigating officers so that they can't be influenced by outside circumstantial facts.