For decades, largely unrealized by judges, many of the forensic practices admitted into judicial proceedings have been without scientific foundation or any other logically acceptable basis other than observational (inductive) study by experimenters untrained in experimental process.Read the rest of this informative column here.
Most troubling are the declarations of certainty associated with proffered expert opinions in those unfounded practices as expressed by examiners in criminal proceedings, such as in firearm/toolmark identification.
Despite the lack of true scientific foundation, firearm/toolmark examiners typically state to a practical certainty that a defendant’s gun was the only possible firearm that could have fired the fatal bullet in a murder. The identification is made on the basis of scratches (striae) and/or impressions on the bullets and comparisons with defendants’ guns.
When examiners confidently declare individualizations (specific source attributions) between crime scene evidence and evidence seized from an eventual defendant without adequate foundational statistical studies, the testimony constitutes nothing more than intuited opinion or speculation, even if an educated guess, rather than evidence-based testimony.
Largely because there has been little or no extrajudicial interest in most forensic practices in past decades other than DNA, forensic procedures such as hair and fiber analyses, bitemarks and comparative bullet lead analysis (CBLA) were developed through empirical induction (observational study) by the practitioners themselves, almost exclusively nonscientists. As noted by a 2009 National Academy of Science committee report, “The fact is that many forensic tests — such as those used to infer the source of firearms or bitemarks — have never been exposed to stringent scientific scrutiny. Most of these techniques were developed in crime laboratories to aid in the investigation of evidence from a particular crime scene, and researching their limitations and foundations was never a top priority.”
Although observational study (induction) is a useful basis for decision-making in everyday life (e.g., purchasing a vehicle or new shoes based on favorable outcomes of past transactions), it is a particularly tenuous process for forensic experimentation or scientific hypothesis testing without appropriate statistical inference.
Sunday, December 30, 2012
'Make forensic evidence meet standards of science'
A Texas A&M professor and former FBI forensic scientist teamed up to author a column in the Austin Statesman today titled "Make forensic evidence meet standards of science." The article opens: