Forensic scientist sticks to his guns

Professor Paul Kirkbride may not be a detective, but he’s on a mission to catch the perpetrators of gun crimes - even when they haven’t left behind a weapon or bullet cartridge.

Formerly the assistant director at Forensic Science SA and chief scientist at the Australian Federal Police, the Flinders University researcher is now employing cutting-edge instruments to examine gunshot residue at a very high level of detail. He explained that the tiny, smoke-like particles “effectively leak out of a firearm when it’s discharged” and may end up on the victim, the shooter or witnesses nearby - but because of their small size, analysis of the particles has, until now, been “quite a challenge”.

Professor Kirkbride’s decade-long search for new analytical techniques gained new ground when he collaborated with the University of South Australia’s (UniSA) Ian Wark Research Institute and was granted access to its time-of-flight secondary ion mass spectrometer (ToF-SIMS). The device was the only one in Australia at the time, and was additionally “not an instrument that a typical forensic lab would be able to afford to buy”, he said.

The UniSA ToF-SIMS. Image credit: Sam Noonan.

Yet the ToF-SIMS, which is typically used for the analysis of mineral particles rather than forensic work, was ideal for Professor Kirkbride’s research. Unlike other scientific instruments, the surface analytical technique allows researchers to work with very small particles and to only sample a very small quantity of materials at any one time.

“It gives us a lot of opportunity to work with a small particle and gives us plenty of time to acquire good data, and the ToF-SIMS, being a mass spectrometer, allows us to identify a wide range of elements that are present in the material we’re analysing,” Professor Kirkbride said.

“It allows us to get down to the level of concentration of around tens of parts per million in a particular material. So it not only allows us to get an idea of the general make-up of something, but also the trace-level stuff, which is often far more informative than the gross level of composition.”

Image credit: Sam Noonan.

Working with his then-PhD student John Coumbaros in a collaboration with Western Australia’s ChemCentre, Professor Kirkbride found that there are two types of gunshot residue: that of the gunpowder (the propellant), which comprises organic compounds like nitro-glycerine; and the primer, which is a primary explosive that detonates when the fire pit hits the cartridge and contains a mixture of various salts and ground glass. Many of these primary ingredients change their composition when the explosive detonates and the gun fires - but the glass does not.

“We have something that carries its composition through from the unfired stage, through to the fired stage, through to the residue stage,” Professor Kirkbride said. “So we recognised that this was actually a residue from the firearm, and that it carries with it unique properties … [and] allows us to form a link, a chemical link, between a residue and the ammunition.”

The project marked a significant milestone in Professor Kirkbride’s career. It helped to close a Western Australian murder case, and Coumbaros went on to become a senior scientist at ChemCentre. Professor Kirkbride, meanwhile, successfully applied for financial support through the South Australian Government’s Premier’s Research and Industry Fund.

The funding was “absolutely vital” to Professor Kirkbride’s research, he said, and has enabled him to utilise a new piece of scientific equipment - this time a Sensitive High Resolution Ion Microprobe (SHRIMP) at Geoscience Australia in Canberra. Manufactured by Australian National University spin-off company Australian Scientific Instruments, the SHRIMP is a huge, high-precision SIMS which is particularly suited to the analysis of oxygen and other stable isotopes.

The SHRIMP from Australian Scientific Instruments.

Professor Kirkbride explained that the identification of stable isotopes in the glass fragments will provide “another level of complexity” to his work. Like the elements in the glass identified by the ToF-SIMS, its isotopic characteristics are like “a fingerprint”, he said, “which doesn’t change before, during or after the gun is fired”.

“The isotope fingerprint carries clues as to the particular geographical origin of the minerals that make up the glass, and we expect that this will point us towards the factory or country of origin of the ammunition,” he continued.

Should it prove successful, Professor Kirkbride’s work will provide obvious benefits to law enforcement. The Australian Institute of Criminology states that 17.5% of homicides in 2012 were carried out using a firearm - only a small drop since records began in 1995 (18.4%) and a fair increase since 2005’s low of 9.6%. The potential to link residue back to its ammunition - and the ammunition back to a suspect - would therefore be an “incredibly valuable - and previously unachievable - piece of information for law enforcement agencies”, Professor Kirkbride said.

Additionally, Professor Kirkbride is simply pleased to have spent so much of his career collaborating with various researchers and up-and-coming PhD students, such as Coumbaros. Having worked in forensic science since 1986, he feels particularly privileged to have watched his students learn, work and continue into the profession.

“It’s fantastic to bring students through and to contribute to the next generation of forensic scientists,” he said. Given the potential impact of Professor Kirkbride’s work on the industry, it’s fair to say that he’s contributed to the next generation of crime fighters as well.