Overstated forensic science a key contributor to false convictions

According to the National Registry of Exonerations, over 150 people were exonerated in 2018. Together, those people spent 1,600 years in prison for crimes they did not commit.

The Registry also found that official misconduct, typically by police or prosecutors, was the leading cause of wrongful convictions. Nearly a third of last year’s exonerations were related to a single officer in Chicago who framed numerous people for drug charges.

Beyond actual misconduct, however, there was another factor that tended to produce a great many false convictions: overstated forensic science findings. That is, forensic analysts exaggerating the certainty of their test results.

Exaggerated hair comparison analysis convicts innocent man

For example, one exoneree was charged with sexually abusing a 2-year-old. A forensic hair analyst wrongly multiplied exclusion values, according to the New York Times .

He testified that there was a 1 in 2,700 chance that one particular hair belonged to anyone other than the victim. He then said there was a 1 in 48 chance (actually a fairly good chance) that a second hair belonged to someone other than the accused. The analyst wrongly multiplied those values and testified that there was only a 1 in 129,600 chance that the two hairs were random.

When lawyers re-investigated the case, the analyst even acknowledged that his testimony was inaccurate. The most he should have said was that the first hair sample could have come from the victim and that the second hair sample could have come from the defendant.

In 2013, the FBI acknowledged publicly that there is no scientific evidence to support this type of hair comparison at all.

Other forensic tests, including DNA analysis, can easily be misused by over-eager forensic analysts. For example, a New York man was convicted even though the amount of DNA collected from the crime scene was too small to be tested. The state claimed it had software that could “amplify” samples that were too small otherwise. Later, a court found that the expert testifying in the case had exaggerated the software’s abilities, and the state abandoned it after the man’s exoneration.

All forensic tests can be tainted by human error

When it comes to forensic evidence, it’s crucial for the defense to challenge not only the test but also the testimony of the analyst. The reality is, mistakes can be made when collecting the evidence, when testing it, and when reporting on the results. Machines can be uncalibrated. The underlying science behind a forensic test may be faulty.

If you’ve been accused of a crime involving forensic evidence, you need to contact an experienced criminal defense attorney right away.