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Study Questions the Reliance on Comparison Testimony at Trial

by Dale Chappell

 The FBI admitted that its hair-sample analysts were wrong 95 percent of the time when comparing hair samples in approximately 3,000 cases. This included 32 death penalty cases.

A 2012 study by the Pennsylvania Innocence Project and the National Association of Criminal Defense Lawyers found that analysts routinely overstated the strength of their findings, yet courts readily accepted such testimony as truth. How did the faulty testimony survive scrutiny? The study provides the answer.

Just like comparison testimony in matching fingerprints or bite marks, the analysis by the experts has been unquestioned—or upheld—based entirely on court precedent, and not science. Courts citing prior cases have allowed comparison testimony to be accepted as unrefuted, rarely evaluating its accuracy.

The problem with comparison testimony is that most of it was developed by cops in their crime labs without any scientific scrutiny, Amelia Maxfield of the Innocence Project said.

These law enforcement experts, usually the FBI, train thousands of state and local law enforcement personnel around the country who then become “experts” themselves, whose testimony is given great weight in the courts.

Exposure of the problems with comparison testimony by these crime lab analysts has led to exonerations in several states, and courts have granted postconviction relief to prisoners based on the exposure.

Maxfield said judges should “analyze the foundational validity of the [testimony], as well as validity as applied by an individual analyst, rather than simply relying on precedent for admission.


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