It seems the police became involved when ANZ bank made a Suspicious Transaction Report about one of Gong's accounts in March 2016.
The police were able to trace the IP addresses of the computers used to make the transactions to physical addresses in Canada linked to Gong.
Then in July 2016, Customs detained Gong at the New Zealand border when he was found with 34 bank cards and more than $10,000 in undeclared cash.
His laptop and phone were cloned by Customs and copies given to the police, who later interviewed Gong. He said the millions of dollars in New Zealand bank accounts were funds from the sale of health products in China.
The police would require a search warrant to clone someone's laptop and phone. But here, they appear to have conspired with Customs to circumvent those protections. And that is simply not what Customs' border search powers are for. They are for "the administration and enforcement of Customs controls at the border", not for undermining due process and the right to be free from unreasonable search and seizure in New Zealand.
The good news is that the new Customs and Excise Act 2018 makes it clear that Customs will only be able to search electronic devices where they have reasonable cause to suspect "relevant offending" - that is, offences related to importing or exporting prohibited goods. The question is whether Customs will actually obey that, or continue to carry out searches at the behest of police in order to allow them to circumvent warrant requirements and harvest data unlawfully.