How reliable is forensic science?

SAN ANTONIO – Four women, known as the “San Antonio Four,” who were accused of sexually assaulting two little girls and were later locked up for 15 years in prison, were found to be wrongly accused based on forensic evidence that was later deemed scientifically inaccurate.

Can we always trust forensic evidence? And how strongly can forensic evidence hold up in court?

Sometimes, the evidence is strong enough to convict people and ultimately sentence them behind bars for years. It's one of the reasons why the “San Antonio Four” spent 15 years in prison.

In 2016, the women were exonerated of the crimes.

Jennifer Laurin, professor at the University of Texas at Austin School of Law, has studied several cases where forensic science has failed. She said this will continue to happen because science is always changing.

“There are many instances where scientific consensus has shifted over time, and sometimes that can implicate earlier conclusions in criminal cases. And that was essentially the claim that was made in the ‘San Antonio Four’ case,” Laurin said.

Laurin said the medical expert in the case originally claimed the scars on the victims were enough forensic evidence to support that they had been sexually assaulted.

Many years later, an expert in the “San Antonio Four” case retracted her original testimony after defense attorneys obtained updated forensic science that deemed the original claims were baseless in terms of medical science.

It's for these reasons that the Texas Forensic Science Commission was formed in 2005. The commission's job is to investigate the integrity and reliability of forensic science in Texas.

Laurin said the role of the commission is important to continue to examine the ever-changing nature of forensic science.

“Science is at its heart about a continuing process of questioning and testing and re-questioning and retesting,” Laurin said. “It is an open-ended and continually evolving process.”

Laurin said the commission continues to update how forensic science can be upheld in court.

She said one example is through a recommendation the group made in a 2017 report. The commission recommended that evidence based on bite mark comparison not be used in criminal cases.

Laurin said the report found that there was not a strong enough foundation behind the use of bite mark comparison.

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