Prosecutors in Missouri and around the country like to present scientific evidence because they know juries find it persuasive, but should they? While DNA sequencing, fingerprinting and firearm rifling analysis are based on long-established science, some other forms of forensic evidence have little in the way of research or data backing them up. This type of evidence is based on what experts call junk science, and it is usually highly subjective in nature. The experts called on to analyze 911 calls or blood spatter patterns draw conclusions after listening to recordings or looking at photographs, but they cannot state with any scientific certainty that their conclusions are correct.
911 call analysis
Police officers and prosecutors who are trained to analyze 911 calls are taught to look out for guilt indicators like pauses, poor word choices and unusual speech patterns. The retired deputy police chief who was the first to promote 911 call analysis claims that these guilt indicators can help police officers to identify criminals, but researchers have found not found much evidence to support his claim. This kind of junk science has been used in more than 100 criminal prosecutions and at least 1,500 homicide investigations, but it is unlikely to be used again. That is because the FBI has advised law enforcement agencies to stop using 911 call analysis.
Blood spatter patterns
The practice of analyzing blood spatter patterns to determine what happened at a crime scene was developed by a criminologist in the 1970s. The approach was seized on by police departments around the country and became a standard part of violent crime investigations, but that was before the National Academy of Sciences cast doubt on blood spatter analysis in a scathing report. Since that report was published in 2009, criminal defense attorneys have successfully appealed several convictions based on blood spatter analysis.
Scientific evidence presented in criminal trials should be subjected to rigorous scrutiny, but that does not always happen. The courts should be very wary of forensic approaches that are not supported by research and data, but they only seem to lose faith in junk science when it is discredited.