Lateral Thoughts Physics World  June 2020

From the lab to the courtroom

(NBS/NIST)

Not many physicists carry a gun to defend themselves against attackers provoked by their research, but that’s exactly what Wilmer Souder once felt the need to do. Since 1911 he worked at the US National Bureau of Standards (NBS) in Washington, DC (today it is the National Institute of Standards and Technology (NIST)), eventually developing forensic techniques that convicted criminals. Souder was not the only forensic physicist in that era. John H Fisher, another ex-NBS physicist, invented a device essential for forensic firearms identification. Both of their contributions were important in major criminal trials and made a sizable impact on the justice system.

Fisher worked at the independent Bureau of Forensic Ballistics, established in 1925, where he invented the helixometer to peer inside the barrel of a firearm without sawing it in half lengthwise. His patent shows the device’s optical arrangement and graduated angular scale that allowed an investigator to examine defects in the barrel and find the pitch of its rifling – the internal spiral groove that imparts a stabilizing spin to a bullet. These features leave unique marks on bullets fired from a given weapon. Along with the double microscope for side-by-side comparison of bullets, invented at that same bureau, the helixometer made it possible to link a bullet from a crime scene to a specific weapon.

Souder’s forensic work was not well known until 2014, when Kristen Frederick-Frost, curator of the NIST Museum, found a forgotten trove of Souder’s old notebooks. She joined forces with John Butler at NIST, whose own work on DNA analysis has contributed to forensic science, and who compiled much of Souder’s work from his notebooks.

Souder earned his physics PhD in 1916, from the University of Chicago. One of his teachers was Albert Michelson, who won the 1907 Nobel Prize for Physics for the precise interferometric measurements crucial to the 1887 Michelson–Morley experiment. Souder’s PhD adviser was experimentalist Robert Millikan, who would earn the 1923 Nobel Prize for Physics, for research on the photoelectric effect and the charge on the electron. Souder published two papers with Millikan, and his dissertation about the photoelectric effect, in Physical Review.

Initially, Souder studied dental materials at NBS, to help the US Army develop treatments for soldiers – a research award in dentistry is now named after him. But another pressing need soon arose, thanks to growing criminal activity in the 1920s. Much of this was fuelled by Prohibition, the era from 1920 to 1933 when the US banned alcoholic beverages, and criminal gangs fought viciously to control illegal bootlegging. Souder’s notebooks show that he responded by providing forensic analysis of handwriting, typewriting and bullets on more than 800 criminal cases for the Department of Justice, the Treasury Department and other agencies. As the NIST researchers discovered, this resulted in an appreciative note from FBI director J Edgar Hoover, and a gun carry permit for Souder (seen above) that was justified protection for a witness in criminal trials.

In 1932 Wilmer Souder was already calling for standards to be established for forensics equipment

These pioneering forensic approaches played roles in major cases. The historical research at NIST showed for the first time that Souder was involved in a sensational 1935 “trial of the century”. It found Bruno Hauptmann guilty of kidnapping and killing the 20-month-old son of Charles Lindbergh, famous for the first solo flight across the Atlantic Ocean in 1927. Souder’s study of the ransom notes in the case, with that of other handwriting experts, provided much of the evidence that put Hauptmann in the electric chair.

Weapons identification was likewise essential in another world-famous trial. In 1921, two Italian-born anarchists, Nicola Sacco and Bartolomeo Vanzetti, were convicted of shooting and killing two men during an armed robbery in Massachusetts. The verdict was widely condemned as having been unjustly influenced by the prevailing anti-radical sentiment in the US. At a final review of the case in 1927, Calvin Goddard, head of the Bureau of Forensic Ballistics, testified that the helixometer and the comparison microscope unequivocally showed that one fatal bullet and a cartridge case came from Sacco’s pistol. Sacco and Vanzetti were executed but controversy continued, although modern bullet analysis has confirmed Goddard’s result.

These early forensic methods remain valuable, but forensic science in the US has lost some of its lustre. Reviews in 2009 and 2016 found that much of forensic practice has developed without the scientific rigour that would make it truly reliable in deciding guilt or innocence. The reviews called for improvements in forensic science, some of which are under way (see October 2019 p43). Souder, well-trained in scientific exactness, would have applauded these recommendations. The NIST researchers found that in 1932 he was already calling for standards to be established for forensics equipment, for precise forensic data and its detailed recording, and for stringent testing to qualify forensics experts.

Souder was also well aware of the difficulties in presenting scientific evidence to judges and juries who lacked scientific training. He used oversized aluminium models of bullets to illustrate ballistic methods, and in 1954, writing in Science, described how to be an effective scientific witness in court. The article ended with Souder’s rallying cry for the value of good forensic science that still resonates: “Justice is sometimes pictured as blindfolded. However, scientific evidence usually pierces the mask.”