The National Institute of Standards and Technology (NIST) recently identified 149 potential sources of human error in the analysis of crime scene fingerprints.  In an article published by NIST, the results of a study by a working group of 34 scientists, NIST recommends changes to reduce human error and make conclusions more reliable.  You can download the report at this site.

Fingerprint evidence is difficult to deal with in trial because the examiner offers his or her "opinion" as if it were indisputable fact. In truth, the examiner identifies a number of points of comparison and then, if similar to the known sample (for example, from our client), declares that the prints "match."  He or she may use fewer than 7 points of comparison in many jurisdictions and still declare the "match."

How do you handle this type of evidence at trial?  Start with NIST article and think about the issue as if it was any other opinion, subject to attack on that basis. Expert opinions are conclusions based on a review of facts (like points of comparison on fingerprints), and are subject to human error. Opinion testimony is also subject to cross-examination for bias (testimony that favors a position) and prejudice (testimony that opposes a position).  For example, an examiner may be part of the "prosecution team," with an agenda to obtain a conviction.  He or she may acknowledge that there are no real standards with respect to how many points of comparison are required to state the opinion. Perhaps he or she has been retained in a case and has been paid for the opinion.  

My point is simple – treat this witness just like any other "expert" and cut away at credibility, in part by focussing some of your cross-examination on human error.

But recognize that jurors love "scientific" evidence.  Science has certainty, or at least the appearance of certainty, for that moment in time. Turns out the earth is not flat – regardless of the opinions offered to the contrary. And maybe that "matching" fingerprint is a match only because the analysts are subject to human error. Jurors will need a reason (or 149) to not believe the conclusion that the prints match, so go slow and go broad. The more potential doubt the expert can concede, the better you will do.