Microscopic Hair Analysis Is Unreliable

Thousands of defendants in both state and federal court may be in jail based on evidence that the United States Justice Department, as early as 1984, knew was unreliable. In many criminal cases, the prosecution uses lab reports produced by forensic experts that link a defendant to a victim or to a crime scene. In a substantial amount of these cases, the forensic reports are based on microscopic hair and fiber analysis done by a forensic expert. In short, an expert will compare a hair strand found at or near the scene of the crime with the defendant’s hair to determine if any similarities exist.

In many cases, however, this analysis has proven unreliable. In the 1990s, after reports that FBI lab results were producing unreliable evidence, the FBI commenced an investigation to determine whether forensic evidence was reliable. One of the problems with this investigation was that it was severely limited to one problematic expert, when the scope of questionable microscopic evidence reaches well beyond just this one individual.

More problematic yet, Justice Department officials stated that when an error is found in a lab report or analysis, prosecutors are not constitutionally or otherwise legally required to inform the defendant directly when they learn of such errors. Of the cases that were investigated, less than half of defense attorneys were notified of the results of the investigation. This raises a substantial issue of whether the government considers unreliable scientific evidence to be exculpatory, which would require the state to disclose the evidence under the federal Constitution.

The problem with hair and fiber analysis

One of the major problems with these lab reports is the inconsistency of hair analysis. Forensic experts will typically consider a variety of factors to determine whether the hair strand found at the scene matches that of the defendant.

The problem with this analysis is that forensic experts do not agree on which characteristics to use nor on how many similar characteristics are necessary to have a statistical match. While some experts relied on six or seven traits, others need around 20 or 30 to determine whether a match exists. One agent concluded that only three similar characteristics, that the hair was black, that it was human head hair, and that it was from an African American, showed the hair belonged to the defendant.

Even if two hair fibers look substantially similar, the FBI has acknowledged that it cannot conclusively prove that the hairs did indeed come from a particular person. For instance, in one particularly tragic case, Sentae Tribble, convicted for murder in 1980 and who has served 28 years in prison, was found guilty in large part because of a stocking cap found a block away from the crime scene. A forensic expert there said that all hairs from the stocking were human and that one of the strands matched Tribble’s based on a microscopic characteristic analysis.

Just this past year, after a long struggle, the hair samples were finally tested for DNA. The results of the DNA testing showed that none of the thirteen hairs on the stocking cap matched his DNA. In further adding to the unreliability of microscopic analysis, the DNA test showed that twelve of the thirteen hair strands were of African origin, while one was from a canine. The FBI agent conducting the microscopic analysis for Tribble’s trial determined that the hair came from a Caucasian; that is, the agent failed to recognize the difference between human and canine hair, yet testified at trial that the hair belonged to the defendant.

Moving forward

The problem with microscopic hair analysis may be less about the procedure and more about the impact and testimony regarding the analysis. For instance, even if two hairs are extremely similar, approximately eleven percent of the time those hairs came from two different people according to Dweight E. Adams, the director of an FBI lab from 2002 to 2006. Despite this, many agents testify at trial that rarely can they not tell the different between two hair samples, or rarely do two hair strands that are extremely similar come from two different people.

Now, criminal defense lawyers are pushing for DNA testing in cases where hair analysis was a key piece of evidence in a conviction, and where the other evidence at trial was very limited. Although Justice Department officials agreed to do a review, they are again limiting the scope of the review, this time to D.C. cases only.

Defending against microscopic hair analysis requires an experienced criminal defense attorney that knows how to properly defend against unreliable evidence that is presented at trial.