The study, expected to be released in the next few weeks, makes about a
half-dozen recommendations to improve the FBI lab's science used to match
bullets through their lead content.
The academy's findings, which are in final draft form, were described
to The Associated Press by several people involved in the study. They
would speak only on condition of anonymity.
The study specifically urges the bureau's chemists to stop a practice
known as data chaining that chemists have used in the past to match
bullets to a crime.
In data chaining, scientists can conclude that if the lead content of
bullet A matches bullet B, and bullet B's content matches bullet C, then
it is safe to testify that bullet A and bullet C are a match even if their
test results don't match identically. Said another way, the FBI can match
two dissimilar bullets if they can find a third — from a manufacturer, for
instance — that matches both.
The FBI science relies on the theory that bullets from the same batch
of lead share a common chemical fingerprint.
Charles Peters, an FBI's expert witness in cases involving bullet lead
comparison, testified recently that data chaining — the technique
disavowed by the academy — was important to matching bullets.
"I'm a fan of chaining," Peters testified in April in a case in Alaska.
"If we had great precision, really good precision ... and we didn't do
something like chaining, or something like that, nothing would ever
match."
A reference in the latest draft of the academy report indicates the FBI
may abandon the data-chaining technique, the sources said. FBI officials
said Thursday night they had not seen the report and could not comment on
it.
"I cannot comment on a draft report that is still being peer reviewed
and subject to change," National Academy of Sciences spokesman Bill
Kearney said Thursday.
Citing specific examples of conflicting or inconsistent testimony by
FBI experts, the study also recommends that lab analysts' work and
testimony be reviewed by a peer to ensure accuracy and precision, the
sources said.
The FBI lab's director has been trying to increase the number of peer
reviews inside the lab.
The academy's recommendations are likely to have a huge impact, opening
the door for appeals from defendants convicted in past cases where bullets
were matched by the FBI using lead analysis. It also could force FBI lab
witnesses to more narrowly describe the statistical significance of their
findings in future cases.
The FBI has been the prime practitioner of lead bullet comparisons in
the United States, and has used it for decades, dating to around the time
of President Kennedy's assassination 40 years ago. A database of lead test
results kept by the agency had more than 13,000 samples in the late 1990s,
FBI officials have told the AP.
The FBI most commonly identifies bullets recovered from a crime by
firing new bullets from the suspect's weapon and comparing the markings
left by the gun barrel on the test bullet with the crime scene bullet. But
that method only works when the crime scene bullet is in good shape or if
police have the suspect weapon.
In cases where recovered crime scene bullets are fragmented or
disfigured or a suspect's weapon is unavailable, the FBI has turned to
chemical analysis to try to determine whether the bullet's lead content is
comparable to the same manufacturer, lead source or box of bullets
connected to the suspect.
When the lab makes a match, its experts testify that two bullets are
"analytically indistinguishable."
FBI Lab Director Dwight Adams earlier this year asked the academy to
review the lead bullet identification process after one of the bureau's
most respected metallurgists, after he retired, began openly challenging
his former employer's science. The FBI paid for the study by the academy,
which is one of the nation's premiere scientific institutions.
The former FBI metallurgist, William Tobin, and his colleagues have
published research stating that bullets from the same lead source had
different chemical makeups and bullets from different lead sources
appeared chemically similar, challenging the very premise of the FBI's
science.
Testifying as a defense expert, Tobin has cited evidence that FBI lab
experts have testified in conflicting manners about how lead composition
can identify bullets and link them to criminals.
Iowa State University has conducted research that drew similar
conclusions.
"The fact that two bullets have similar chemical composition may not
necessarily mean that both have the same origin. ... The leap from a match
to equal origin is enormous and not justified given the available
information about bullet lead evidence," Iowa State researchers reported.