Say Goodbye to Lead Bullet Analysis
Actually, the goodbyes to this forensic technique began in 2005, when the FBI announced that, after extensive study and consideration, it would no longer conduct the examination of bullet lead, but a joint project of the Washington Post and 60 Minutes seems to be the final nail in the coffin of lead bullet analysis.
Here’s the gist of the technique as described by ScienceNews in 2004:
First developed in the 1960s, bullet chemical analysis has been used
by prosecutors when a suspect’s weapon is not available or when the
bullet found at a crime scene is too fragmented to permit visual
inspection of the characteristic markings that firearms leave on intact
The chemical analysis consists of measuring seven trace
elements—arsenic, antimony, tin, copper, bismuth, silver, and
cadmium—that typically are present in a bullet’s lead alloy. Each
element makes up less than 1 percent of the total lead alloy.
Using a technique called [inductively coupled
plasma–optical–mission spectroscopy]5, a forensic chemist determines the
proportion of each element in the lead alloy. In that analysis, the
chemist dissolves a sample of the bullet and feeds the resulting
solution into the instrument’s plasma chamber, where each element in
the sample emits specific wavelengths of light. The pattern of
emissions serves as a fingerprint for that element, so the intensity of
the light of each pattern indicates how much of the element is present.
The problem is that, as this handy schematic illustrates in somewhat simplistic terms, matching bullet composition does not necessarily prove a shared source – and that means folks like Lee Wayne Hunt, who claims he was wrongfully convicted of murder as a result of lead bullet analysis, may be right, and may soon be freed. The joint investigation by WaPo’s John Solomon and 60 Minutes’ Steve Kroft identified, Solomon writes, “approximately 250 cases nationwide in which bullet-lead analysis was introduced, including more
than a dozen in which courts have either reversed convictions or now
face questions about whether innocent people were sent to prison.” This after the Bureau stopped performing the analysis in 2005, and this after concerns were expressed as far back as 1991.
There’s lots to watch develop but for those who need a bottom line, here it is: bullet lead analysis became an FBI forensic staple after the technique seemed to confirm that Lee Harvey Oswald acted alone in assassinating John F. Kennedy. Now, maybe not so much…