The fate of Canberra's cannabis laws will come down to legal arguments over one of Europe's biggest tax scandals involving the theft of bank records of some of the world's biggest tax evaders.
Incongruous as that sounds, it is where the confusion over whether cannabis will or will not be legal on January 31 has landed. The ACT's Legislative Assembly has made it legal from the end of January for adults to grow and use cannabis. The federal government, though, says because cannabis remains illegal under federal law, Canberrans will still be able to be prosecuted and face hefty fines or jail.
When Commonwealth Director of Public Prosecutions Sarah McNaughton was asked in Senate estimates why she had changed her mind on the legal status of cannabis, she said it was because the Attorney-General's Department had drawn her attention to a Queensland tax case.
That case turns out to involve records stolen in 2002 from Liechtenstein's LGT bank by a former employee, Heinrich Kieber, often described as a whistleblower and now reported to be living, possibly in Australia, under an assumed identity provided by German authorities to whom he sold the records.
Mr Kieber provided the records to Australian tax authorities, who expected to recover $100 million from 20 separate accounts held by Australians, according to a Four Corners report in 2008.
Among them were Kevin and Helena Denlay, a northern NSW couple who ended up in a protracted legal fight with the tax office.
In fighting the tax office, Kevin Denlay argued in the Federal Court that because the Lichtenstein bank records had been obtained illegally they could not be used by the tax commissioner against him. He lost.
So if people are allowed to possess and grow cannabis under ACT law, they should be able to use that as a defence against the federal law that criminalises it.
The criminal code has a similar provision for federal laws - allowing criminal conduct that is "justified or excused by or under a [federal] law".
In the tax case, the Denlays tried to argue that there was no law that allowed the tax office to receive information stolen overseas. But the courts found that there was - the tax law that gives the commissioner full access to any relevant buildings, books, documents and papers.
In what appears to be the relevant sentence in the Denlay judgement, the full Federal Court said there might not be "specific legal authority" for the commissioner to access the information overseas.
"There is, we think, something to be said for the taxpayers' argument that, if specific legal authority were necessary to make access to the information provided by Mr Kieber lawful in the overseas location where that occurred, then s263 [of the tax law] did not provide it," the full Federal Court commented.
The court said it wasn't necessary to resolve that question.
But essentially, that appears to be the source of the Morrison government's claim now that the courts might need "specific legal authority" to make something illegal that would otherwise be illegal.
If that does turn out to be the case, the question becomes whether that specific authority has been provided under ACT law to possess cannabis.
The federal government says not. The Commonwealth Director of Public Prosecutions initially said the ACT law justified the possession of cannabis, so she wouldn't prosecute because cannabis possession was excused under ACT law.
The ACT government appears to be saying bring it on. It has so far given no indication that it will amend its law to create a specific legal authority, but instead is challenging federal authorities to test it in court.
Jeremy Gans, a professor in criminal law at Melbourne Law School, said the Denlay case was "hardly a clear decision and it's certainly not determinative".