[ 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)