Tokyo - Japanese police arrested three people on Wednesday in connection with the 1995 shooting of the country's top police official. The police identified the suspects using the massive SPring-8 synchrotron, a powerful X-ray beam that can reveal the chemical makeup of tiny samples.
The three are all former members of the Aum Shinrikyo cult, which on 20 March 1995 released sarin nerve gas on the Tokyo subway, killing 12 people. Ten days later Takaji Kunimatsu, then head of the National Police Agency and leader of the investigation into the attack, was shot and critically injured.
The smallest traces of metal from a fired bullet can be analysed with a synchrotron.
The key new evidence is reported to have come from analysis of metal traces found on one suspect's clothing. Impurities in this metal are believed to match those in the gun used to shoot Kunimatsu. The police have refused to make any statements, and the name of the scientist leading the new investigation is being withheld to protect his or her safety.
The police wouldn't have a case without SPring-8, says Akito Kakizaki, a physicist at the University of Tokyo. SPring-8, the world's most powerful synchrotron, can analyze samples weighing only trillionths of a gram - which, in criminal evidence, is often all that is available.
This is not SPring-8's first contribution to forensic science. In December 1998, evidence from the synchroton helped convict a woman suspected of killing four people at a festival by putting arsenic in a curry.
Ten milligrams of arsenic found at the suspect's home matched the chemical added to the curry. The synchrotron revealed matching bismuth and antimony impurities in the two samples.
"Conventional methods of analysis would need much more [arsenic]," says the scientist behind that analysis, Izumi Nakai, an analytic chemist at Tokyo University of Science and a member of the American Academy of Forensic Sciences, who is not involved in the current investigation. He thinks the police will use the method more in the future.
Also, synchrotron radiation leaves the sample intact. "We can repeat the experiment many times," says Nakai. "This is extremely important for investigating crimes."
Nakai became involved in the poisoning case through his study of arsenic in hair samples. He is now pushing for synchrotrons to become a staple of forensic science. For example, SPring-8 could identify the glass left behind at a hit-and-run accident or the source of confiscated marijuana, he says.
So far his efforts to get a dedicated synchrotron for forensic science have failed, but he is hopeful. "All countries will begin to use synchrotron energy for forensics," he says.
Only two other synchrotrons could handle samples as small as those in the shooting case: the US Advanced Photon Source at Argonne National Laboratory, Illinois, and the European Synchrotron Radiation Facility in Grenoble France. "With a machine any less powerful it would be difficult," says Kakizaki.