Any prosecution in the shooting death of an Australian security guard at the Baghdad embassy would likely have to use an untested law passed in the wake of the 2002 Bali bombing, legal experts have said. 
As Australian Federal Police investigators returned home from Iraq, law experts said the simplest option available to authorities would be to employ the law against "harming Australians", which makes it an offence to kill Australian citizens overseas.
Chris Betts, 34, died from a gunshot wound at the security contractors' accommodation building next to the Australian embassy in Baghdad earlier this month. It has been widely reported the shooting was witnessed by colleague Sun McKay, 39.
Both men worked for contractor Unity Resources Group and were previously Australian soldiers.
The AFP sent a team of investigators to Iraq and interviewed Mr McKay, but a spokesman told Fairfax Media it "can confirm officers sent to Baghdad to investigate the death of a security contractor have now returned to Australia".
He added that "the investigation into this matter remains ongoing". No charges have been laid.
It is understood Mr McKay has also returned to Australia. A man who answered the phone at Mr McKay's parents' home in Adelaide declined to speak to Fairfax Media.
Ben Saul, a professor of international law at the University of Sydney, said the simplest way for authorities to launch any prosecution should somebody be charged would be under the "harming Australians" provision, which was passed in 2002 after Bali bombings and was primarily intended for terrorism cases.
"That would be the easiest route for the AFP," he said.
Criminal barrister David Neal, SC, said he believed the "harming Australians" law could be used.
Two other lawyers who spoke to Fairfax Media but asked not to be named agreed it could be used.
Because the death happened in Iraq, it is unlikely any murder or manslaughter prosecution could be launched in Australia, unless the defendant had diplomatic immunity, in which case Australia law applies to them.
But the "harming Australians law", part of the Commonwealth Criminal Code, effectively contains equivalents of murder, carrying a penalty up to life imprisonment, and manslaughter, carrying up to 25 years' jail.
It appears not to have so far been used in any prosecution, based on searches of Commonwealth law databases.
The law was was amended late last year following a push by Industry Minister Christopher Pyne and South Australian independent senator Nick Xenophon to backdate it so it could be applied to the 1994 murder of Adelaide woman Anthea Bradshaw-Hall in Brunei.
Senator Xenophon has called for a full inquiry into the shooting of Mr Betts in Baghdad.
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