An inves­ti­ga­tion by The Washington Post and 60 Minutes has cast doubt on at least 250 crim­i­nal cas­es in which the defen­dant was con­vict­ed based on FBI bul­let-lead test evi­dence. Since the ear­ly 1960s, the FBI has used a tech­nique called com­par­a­tive bul­let-lead analy­sis on an esti­mat­ed 2,500 cas­es, many of which were homi­cide cas­es pros­e­cut­ed at state and local lev­els. Comparative bul­let-lead analy­sis, based on the assump­tion that all bul­lets in one batch will be chem­i­cal­ly sim­i­lar, exam­ines the chem­i­cal com­po­si­tions of bul­lets to deter­mine if crime-scene bul­lets match bul­lets in a suspect’s pos­ses­sion. FBI labs have since con­clud­ed that all bul­lets in a sin­gle batch are not always chem­i­cal­ly matched ​“because sub­tle chem­i­cal changes occurred through­out the man­u­fac­tur­ing process.”

FBI con­cerns over com­par­a­tive bul­let-lead analy­sis were first doc­u­ment­ed in 1991, and a study by two for­mer FBI lab tech­ni­cians chal­leng­ing the tech­nique was com­plet­ed in 2001. In 2004, the National Academy of Sciences also reject­ed com­par­a­tive bul­let-lead analy­sis, stat­ing ​“that decades of FBI state­ments to jurors link­ing a par­tic­u­lar bul­let to those found in a sus­pec­t’s gun or car­tridge box were so over­stat­ed that such tes­ti­mo­ny should be con­sid­ered ​‘mis­lead­ing under fed­er­al rules of evi­dence.’” A year lat­er, FBI lab direc­tor Dwight Adams rec­om­mend­ed to FBI Director Muehller that the Bureau aban­don the com­par­a­tive tech­nique and dis­cour­age pros­e­cu­tors from using it in future tri­als.

Adams believes that the gov­ern­ment has an oblig­a­tion to review cas­es in which the tech­nique was used and to noti­fy courts of any con­vic­tions that could have been erro­neous­ly based on the tech­nique. ​“It trou­bles me that any­one would be in prison for any rea­son that was­n’t jus­ti­fied. And that’s why these reviews should be done in order to deter­mine whether or not our tes­ti­mo­ny led to the con­vic­tion of a wrong­ly accused indi­vid­ual,” Adams said to the Post. ​“I don’t believe there’s any­thing that we should be hid­ing.”

The Post and 60 Minutes con­duct­ed a nation­wide inves­ti­ga­tion, research­ing court files and hold­ing inter­views with dozens of lawyers and sci­en­tif­ic experts. Their research yield­ed at least 250 cas­es in which evi­dence from com­par­a­tive bul­let-lead analy­sis was intro­duced. More than a dozen of these con­vic­tions have been reversed or are now being chal­lenged as to whether inno­cent peo­ple were sent to prison.

The FBI has said it would con­duct a nation­al review of these cas­es and cre­ate a sys­tem where future sci­en­tif­ic tes­ti­mo­ny can be monitored. 

(“FBI Forensic Test Full of Holes” by John Solomon, The Washington Post). Read the series here.

See also Arbitrariness and Innocence.

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