Shelling Out Evidence: NIST Ballistic Standard Helps Tie Guns to Criminals

[ Music, Sound of
gunshots heard, followed by crime scene noise ] Narrator: gunshots are fired
…a crime is committed …the suspect escapes The evidence
left behind could help bring the shooter to justice. Probably … that evidence will
include one of the more than 200-thousand shell
cartridge cases retrieved each year at crime scenes in the
U.S. To the trained staff of a forensics lab … a recovered case is like
a ballistic fingerprint. That’s because firing a
gun leaves a unique pattern of marks impacted on the
surface of the shell. Known as a case signature … this pattern can be
compared to thousands stored in a national database. If there’s a match … a forensics lab can identify
the specific firearm used in a crime. That is … if they can prove
the match is accurate so that the finding
holds up in court. Thanks to the national institute
of standards and technology … that task just got
a little easier. Robert Thompson: Crime
laboratories are increasingly under pressure to show that they
follow good standard practice, to show accuracy in
their examinations. In the firearms identification
laboratories, NIST has given them
the opportunity to use a standard bullet about
seven years ago, and now, we’ve just rolled out a standard
cartridge case for them to use. Narrator:The new NIST
standard started its life when the agency acquired a
cartridge case from the bureau of alcohol, tobacco and firearms
that had distinctive examples of the three most
important case signatures: the firing-pin impression
…the breech face impression and the ejector mark. To make identical
copies of this case and its markings …NIST’s
forensic scientists turned to a technique known
as electroforming. Similar to the method by
which jewelers cover objects with silver or gold … electroforming was used to
surround the template case with a thick metal coating. Once the coating solidified and
the shell inside was removed … a nearly perfect negative
mold was left behind. Alan Zheng: When I first
received the replica cases, I compared them to
the master casings that they were produced from. And to my eyes, I could not tell
any difference between the two. That’s because the mold is so
accurate that it is able to pick up feature sizes
100 times smaller than the width of a human hair. Narrator: Along with producing
the replica cartridge case … NIST and the ATF also
captured its signature marks in digital images taken with
the same type of microscope used to enter case signatures
into the national database. For accuracy … a forensic lab can compare
these “golden images” to ones they acquire of
the NIST replica case. If they match … the staff can rest assured that
their results will be in sync with all other forensic
labs that use the standard. Together … the replica shell cases and
the golden images combine to make a powerful
crime fighting tool … NIST standard reference
material 2461. Brian Renegar: For instance, let’s say there was a crime
committed in California and there maybe was
another crime committed in New York city, and
the examiners wanted to compare the evidence to
see if there was a match between the two crimes. one way they can do this is
by using a national database to correlate the
images together. however, they need something to make sure there’s
quality control that the images were
acquired correctly and that’s where the NIST standard
casing comes in.” Narrator: After all … NIST and its partners in law
enforcement want to make certain that criminals who use
guns don’t get away with their crimes. (Music out at fade to black)
(Music up and under credits)