Forensic science evidence can be flawed, misleading, remarkably unscientific, and sometimes flat wrong.

Attorney General J.B. Van Hollen was right recently when he declared, "Murderers should fear forensic science." Forensic science evidence can be a powerful tool against the guilty. It has also proven to be a powerful tool for exonerating the wrongly accused and convicted.

But in our exuberance to embrace the wonders of forensic science, we must be careful not to be swept away too readily by any claims presented in the guise of "forensic science." As effective as forensic science evidence can be, it can also be flawed, misleading, remarkably unscientific, and sometimes flat wrong.

Indeed, examination of the nearly 260 DNA exonerations of the last two decades reveals that misleading or erroneous forensic science evidence has been the second most prevalent contributor to wrongful convictions - second only to mistaken eyewitness identification. And a recent analysis of DNA exoneration cases found that prosecution forensic analysts gave invalid or inaccurate testimony in 60% of the trials studied.

It is thus with some irony that Van Hollen celebrated the power of forensic science evidence in a press release about a court of appeals opinion affirming a conviction in a case that included some of the most suspect and least-scientifically grounded forensic "science" testimony possible. In that case, a ballistics expert visually matched a bullet from a murder to the defendant's gun, and testified that no "other gun in the world would have left those particular type of markings on that bullet." He added, "There is no error rate" for his "eyeball analysis."

Ballistics can be a useful tool in identifying sources of bullets from a crime scene. But there is no basis in science for proclaiming that a particular bullet could be matched to a particular gun to the exclusion of all other guns. There is no scientific basis for such assertions because they have not been studied adequately. No scientific principles define how many points of similarity must be identified to call a gun and a bullet a match, or even what protocols analysts should employ when making their visual comparisons.

And certainly no scientific analysis supports the analyst's claim that his method has no error rate. No real science, not even DNA analysis, can claim such perfection.

This is precisely the type of indefensible testimony that sent Robert Lee Stinson to prison for 23 years for a Milwaukee murder he did not commit. In that case, the expert (a forensic dentist) proclaimed that he had matched Stinson's teeth to bite marks on the deceased's body, to the exclusion of all other teeth in the world. DNA not only exonerated Stinson 23 years later, but also identified the true perpetrator.

And it is precisely the kind of testimony that the National Academy of Sciences decried recently as unsupported by scientific evidence and grossly improper.


Link: http://www.jsonline.com/news/opinion/102105579.html