Subatomic particles travelling at near the speed of light is the last thing you’d expect to find use in a forensic scientist’s toolkit.
But that’s exactly what cracked the case of a murder in Perth in 2007. Australian scientists used a high-energy synchrotron beam to trace microscopic brick fragments to their origin. They have recently received permission to reveal how it was done.
The body of a West Australian Supreme Court registrar Corryn Rayney was discovered buried, face-down, in Perth’s Kings Park in August 2007, after she had failed to return home a week earlier following a line dancing class at a nearby Community Centre.
After a year of investigation, police had failed to establish the scene of the murder as they asked Robert Fitzpatrick and his team from the Centre for Australian Forensic Soil Science at the Commonwealth Scientific and Industrial Research Organisation to step in.
Taking a detailed look at Rayney’s clothes, the scientists discovered millions of previously unnoticed microscopic red particles lacing the victim’s bra strap – brick particles which could not found at the Community Centre or near the gravesite.
The team attempted to identify the origin of the bricks by analysing the minerals inside the fragments, using a technique called X-ray powder diffraction.
Because different minerals scatter light in a different way, samples glues to a thin glass fibre and placed in front of an X-ray laser produce what Fitzpatrick refers to as a characteristic “fingerprint”.
However, the size of the particles found in the bra strap was too small for their laboratory X-ray source to produce a signal strong enough to distinguish a fingerprint between different samples.
It wasn’t until they exposed the brick fragments to the high-energy X-ray beam at the Australian Synchrotron that they discovered their samples were a smoking gun.
This synchrotron, which was opened a week before the Rayney murder, creates the high-energy beam by accelerating electrons around a 216-metre ring to near the speed of light, using powerful magnets. These electrons emit electromagnetic radiation which the synchrotron’s instruments can concentrate to a powerful X-ray laser.
“It was just phenomenal,” Fitzpatrick recalls. The diffraction signals, stronger than their lab experiments’, revealed the mineral composition of the brick particles which the team compared to brick samples from the Rayney home and the Community Centre.
Their synchrotron data, he says, let them assign the brick fragments to different mineral groups “with much more confidence”.
This evidence convinced a Supreme Court judge in August 2012 that brick fragments in Rayney’s bra strap matched the front driveway of her residence. The team managed to even narrow down the individual brick which was the source of the particles.
The work has set a precedence, as the first evidence of its kind to be accepted by a court in Australia, says Fitzpatrick.
He believes the Australian Synchrotron will be employed for forensics in future, if the size or amount of the samples warrant it.
“You don’t need a sledgehammer to crack a nut,” he says. “You need to know that it will give you more information.”
But “before, we would have said: ‘No we can’t do this work, it’s too small a particle,’” he adds. “Now, this [method] provides an opportunity to say: ‘I think we could actually go to the synchrotron and have a go.’”
A review of the Rayney case was announced last May, however the current status of the case is unknown.
Fitzpatrick and his team will present their method at the 5th International Conference on Criminal & Environmental Soil Forensics held in Cape Town this August.
Viviane Richter is a freelance science writer based in Melbourne.