Bullet 'fingerprints' to help solve crimes

Jul 30, 2014 by David Stacey
Bullet 'fingerprints' to help solve crimes

Criminals don't just have to worry about their own fingerprints these days: because of a young forensic scientist at The University of Western Australia, they should also be very concerned about their bullets' unique 'fingerprints'.

Anna Bradley (29) of Como is undertaking the world's largest lead study, building on research the FBI started when US President John F. Kennedy was assassinated in 1963.

"Around 20 per cent of homicides and armed robberies in Australia involve the use of a gun," she said. "But if the firearm is not recovered or the bullet is fragmented, this can make things tricky for the physical examination. If a bullet from a crime scene can be 'fingerprinted', which means determining its elemental composition, then it can be compared to the composition of found in the suspect's car or house or in a recovered firearm."

Anna, who is studying at UWA's Centre for Forensic Science, is soon to submit her PhD in which she shows that by being able to determine up to 19 trace elements found in bullet lead - including arsenic, gold and mercury - she can trace a bullet back to its batch of origin, no matter where it was manufactured or where the lead was sourced. After shooting slaughtered pigs' heads with different ammunition, x-raying the skulls, extracting the lead shot and bullet fragments, Anna was able to match the extracted samples to their unique production batch with 97 per cent accuracy.

The FBI only determined seven elements present in bullet lead and dropped the practice of compositional analysis in 2005 because it lacked robustness - but Anna's improvements to bullet lead provenancing may see them adopt her methods.

Anna enlisted the help of two Australian ammunition manufacturers - one big, one small, each with different ways of making bullets - to test her hypothesis and found that the elemental signature of bullets remains unchanged throughout the manufacturing process. She also collaborated with the Western Australia Police Service who provided reference ammunition to build up a data base of different bullets.

"The ammunition I was most excited about analysing was three boxes of unopened military cartridges from 1942, wrapped in twine and date-stamped. We found they had many similarities with modern ammunition, not surprisingly, as bullets are often made from recycled lead."

Anna knew she wanted to be a forensic scientist when, at 15 and living in a small New Zealand town, she and her twin sister Sarah would spend time in the town library after school. "Sarah read the teen romances and I read about serial killers - who they were, how they were caught. I didn't really study chemistry at high school but at Uni I discovered I was quite good at it - and decided to come to UWA to do a Masters and PhD in ."

Explore further: Lead in hunting bullets is dispensable – study proves suitability of alternatives

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User comments : 7

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antialias_physorg
5 / 5 (1) Jul 30, 2014
After shooting slaughtered pigs' heads with different ammunition, x-raying the skulls, extracting the lead shot and bullet fragments,

That sounds like a fun workday.
tadchem
not rated yet Jul 30, 2014
"97 per cent" may be adequate to build a 'consensus' among a small group of people, but any competent lawyer could pick it to pieces in a courtroom that allows 'reasonable doubt'.
btmatsci
not rated yet Aug 11, 2014
This article is rife with fallacies of presumption & unfounded assertions. I'm quite surprised that a university is allowing a Ph.D based on junk forensic practice. Surprising, after the National Academy of Sciences report (2004) and the FBI's public announcement vacating the practice, that some (even in the scientific community) still don't get it.

Seems the university faculty, the author, & Ms. Bradley herself apparently believe that more analytes must mean the ability to discern purported "uniqueness". Worse, the practice was stopped not primarily because uniqueness of composition had never been scientifically established to exist (which it hasn't), but rather because there has never been any study establishing probative value of a claimed "match" of composition. None.

More in follow-up comment.
btmatsci
not rated yet Aug 11, 2014
Follow-up:

See Cole, Tobin, et al., "Retail Sampling Approach to Assess Impact of Geographic Concentrations on Probative Value of Comparative Bullet Lead Analysis", available at http://papers.ssr...1161769.

There are downloadable papers available on the subject on my SSRN author page: my SSRN Author page: http://ssrn.com/author=1521077
btmatsci
not rated yet Aug 11, 2014
tadchem, you're spot-on correct. That was one of the problems included in the fallacies of presumption inbued in the article: drawing universal conclusions from miniscule sample pools. Same flaw with forensic "proficiency tests" (most frequently 3 to 6 pool samples), where "test" results are offered as measures of practice accuracy.

The claim of "97%" accuracy is suspect on several levels. I reject the claim as meaningless, and possibly scientifically unfounded for the purpose for which the author and Ms. Bradley offer it. First, if that figure was developed by deductive inference, then what was the size of the sample pool and why is it being offered as a universal metric of accuracy? If it was developed by inductive inference, then what is the confidence level?

Ms. Bradley hasn't lived long enough, nor does the University have sufficient resources, for proper analytical sampling to have been conducted to support claims of 'uniqueness' or probative value.
btmatsci
not rated yet Aug 11, 2014
This "project" appears to be heading down the exact, 'primrose path' that the FBI did 40 years ago with the same nonscientific, flawed reasoning. Developers of the FBI practice were not true scientists and had no training in the scientific method or proper inductive inference. Contrary to claims about the FBI's alleged "research", the seminal flaw is that they did absolutely no scientifically acceptable "research" establishing either that melt chemistries are 'unique' or that there was any probative value in claimed "matches." They never cared whether everyone with bullets in a community where a shooting occurred may have owned bullets of indistinguishable composition or who else may have purchased bullets from the same retail outlet. For some idea of batch (pot) size, typical heats (pots) of molten bullet lead can produce 39 to 54 million bullets of .22 caliber, the most popular caliber on the market.
Captain Stumpy
5 / 5 (1) Aug 11, 2014
"97 per cent" may be adequate to build a 'consensus' among a small group of people, but any competent lawyer could pick it to pieces in a courtroom that allows 'reasonable doubt'.
@tadchem
@btmatsci
depends on how it is used
if it is the ONLY tie to the suspect? yep... a good defense lawyer might be able to introduce reasonable doubt
however
a "good investigator" will only use the data as a good lead into other area's.

likely there would not be enough to prosecute on the lot/type evidence alone, but it can be used: give enough reason/cause for more investigation and warrants for search

I don't know that it even "can" be used in and of itself for prosecution...
this is just another tool in the investigator's bag of tricks to find the truth.
there are FAR too many possible matches that can be made going by lot type/make alone to justify a prosecution, BUT there is enough along with other evidence to justify a search warrant.