By Sue Russell

Scientists are accustomed to a landscape of shifting knowledge, while the justice system prizes certainty. But the criminal justice system, including forensic science, increasingly has been called upon to re-examine past certainties and to revisit what they once believed to be incontrovertible facts.

Take “comparative bullet lead analysis,” a technique used since John F. Kennedy’s 1963 assassination that “matches” a bullet or bullet fragments to a box or batch of ammunition manufactured at a specific time and place. The chemical analysis behind it hinged on what proved to be a false premise: that each batch of lead had a unique elemental makeup. In 2005, the FBI voluntarily abandoned the technique and every past conviction that conceivably turned on the analysis had to be reviewed.

The conviction of Jimmy Ates was the first thrown out after the FBI’s decision. A jury had found Ates guilty of the 1991 murder of his wife, Norma Jean; she had been shot seven times and their home was set on fire. For years prosecutors wrestled with what they felt was a lack of evidence. When they eventually tried Ates in 1998, among the evidence they did present was comparative bullet lead analysis.

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Source: Pacific Standard