Imagine that you are part of a jury overseeing a murder trial, and the defendant swears he is innocent. The prosecutor calls to the witness stand a forensics expert with more than 30 years of experience in crime laboratories running tests for cases just like this one. The expert brings the jury’s attention to bullet casings found at the crime scene, specifically the tiny marks engraved on the back of each casing. He explains that these are called “bunter marks,” and they are usually impressed on each bullet by the manufacturer during production.
The expert then reveals that, after rigorous testing, the bunter marks on the casings at the crime scene match almost exactly to marks from a box of cartridges found in the defendant’s home. Murmurs spread throughout the courtroom. When pressed about his confidence in the findings, the expert claims he can match the two bullets’ marks with an error rate of less than 1%. Jury members exchange looks. Certainly, this can’t bode well for the defendant.
But despite what the prosecutor would have you believe, Dr. Clifford Spiegelman says this kind of evidence is statistically meaningless. “The same bunter marks can appear on hundreds of thousands, if not millions, of bullets,” he said. Because the same bunter tools are commonly used for large quantities of bullets, matching bunter marks cannot be statistically relied upon to track bullets back to the same box. “Trial evidence will focus on whether or not they can tell it’s the same bunter mark on two different bullets, but statistically, it doesn’t matter if they can.”
Pro Bono Statistician
A distinguished professor of statistics in the Texas A&M University College of Science, Spiegelman has used statistics to address issues in unexpected fields for more than 40 years. He co-wrote a leading textbook in transportation statistics, was named the official statistician of the Texas Holocaust and Genocide Commission, and helped found the interdisciplinary field of chemometrics, which uses statistical methods to better understand chemical data.
Spiegelman’s most publicized work, however, is in forensic science. He is a key statistical adviser to the City of Houston’s crime laboratory. Working with the Innocence Project, a free nonprofit legal organization for wrongly convicted people, he has testified pro bono on cases in which shaky forensic methods, like bunter mark analysis, were being used against innocent defendants.
“People like flashy science,” Spiegelman said. “But doing simple science well is very hard.” In the bunter mark example, for instance, what mattered to the case was not that the bullets had the same bunter mark, but whether that information was statistically meaningful in proving or disproving the defendant’s innocence.
Many similarly flawed forensic methods are still used and treated as iron-clad evidence in criminal courts, motivating Spiegelman to research different methods’ validity. In 2007, his expertise was used to help evaluate the effectiveness of comparative bullet lead analysis, a forensic method first used in the investigation of President John F. Kennedy’s assassination. He and five other researchers assessed the method the best way they knew how: by investigating its use following the JFK assassination itself.
After the Kennedy assassination, it was generally agreed that, given the timeframe and the bolt action rifle assassin Lee Harvey Oswald used, it would have been physically impossible for him to fire more than three times (assuming he was actually aiming before he fired). However, bullet lead found at the crime scene did not definitively indicate the number of shots fired. If there was evidence of a fourth or even a fifth bullet, it would scientifically disprove the theory that Oswald acted alone in killing the president.
A chemist from the House of Representatives Select Committee on Assassinations claimed that each bullet was chemically unique. He used a then-new technique now called “comparative bullet lead analysis” to distinguish the chemical makeup of each fragment. From this, the chemists claimed that the lead fragments came from just two bullets. Stuart Wexler, a New Jersey high school social studies teacher and close colleague of Spiegelman’s, knew that Spiegelman was giving talks about the flawed testimony and recruited him to further investigate.
Spiegelman collaborated with another statistician, two chemists, a metallurgist and Wexler to analyze 30 bullets that were produced from the same manufacturing lots believed to have made the bullets used in the assassination. Scientists at the Texas A&M Elemental Analysis Lab used neutron activation analysis, a process of irradiating the bullets, to measure their chemical composition. Spiegelman and the statisticians then compared the data from each bullet’s measurements against one another.
Their results were conclusive. Of the 30 bullets analyzed, 29 chemically matched another in the same batch, effectively disproving the theory that each bullet carried a unique chemical fingerprint. The 30th bullet was chemically indistinguishable from assassination fragments. By the team’s findings, theoretically there could have been as many as five bullets contributing to the Kennedy assassination evidence. The House Select Committee was misled by the chemist’s testimony. While the team’s study did not prove the presence of a second shooter, it did invalidate a significant piece of evidence supporting the theory that Oswald acted alone.
Bringing Belated Justice
The bullet lead analysis study received local, national and international publicity for its relation to Kennedy’s assassination (and the myriad conspiracy theories around it). Spiegelman himself made more than a dozen appearances on media outlets such as Fox News, CNN and NBC Nightly News. Despite the rotating press coverage around that particular study, Spiegelman’s interests still reside in using statistics to achieve justice for everyday citizens.
Growing up in suburban Long Island, New York, during the civil rights movement, Spiegelman saw the effects of racial injustice firsthand. Decades later, he is helping push for a bipartisan measure that could bring closure, if not justice, to families affected by hate crimes in the 1960s.
“The people who committed hate crimes were often not upstanding citizens outside of those crimes,” Spiegelman said. Many perpetrators of racial violence, for example, also committed burglaries and petty crimes. “But when they were caught and punished for other crimes, their fingerprints were never entered into a database.”
Spiegelman is working with Wexler and U.S. legislators on potential bipartisan legislation that would enter existing forensic evidence collected from the civil rights era into forensic databases, setting a “trap” for former hate criminals still living across the country. Such a database could bring those criminals to account; barring that, it could help close decades-long cold cases.
Lies and Statistics
At a time in which the average American is bombarded with conflicting information daily, Spiegelman has one simple piece of advice when it comes to published statistics. “Be skeptical,” he said. “The numbers you are being fed aren’t always wrong, but they’re often not based on good science.” He pointed to a 2005 study by Dr. John P.A. Ioannidis that claimed most published research findings were often significantly influenced by bias, flawed methodology and financial interests.
Still, in spite of Spiegelman’s caution with regard to published data, his own work proves there is plenty of truth to be found in statistics. His scrupulous attention to detail has helped to free innocent people, reevaluate history and develop sharper analytical tools for society. Spiegelman lives his life by the numbers, and the results speak for themselves.
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Office Hours with Dr. Spiegelman
What are your hobbies?
“Swimming, ranching and working with all kinds of animals, from buzzards to domestic animals.”
Your office is decked out in Minion decorations. What do you like about Minions?
“The Minions represent naivety and manage to stumble their way to success.”
What actor would you choose to play you in a movie?
“Basil Rathbone from ‘The Hound of the Baskervilles’ (1939), based on the Sherlock Holmes novel by Sir Arthur Conan Doyle.”
If you could talk to any scientific figure(s), dead or alive, who would they be?
“Galileo Galilei, to understand how such a courageous person established much of the scientific method in the face of persecution, and Marie Curie, to talk about how she approached science.”
What is the best advice you have for an undergraduate student?
“Learn as much as you can about everything, including the sciences and humanities. The more you understand, the more useful you will be. Lose any sense of entitlement you might have, and plan to work your way to the top.”
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Written by Bailey Payne ’19