Both were revealed this week to have New Zealand-based foreign trusts, corporate vehicles that critics say can help the world's wealthy avoid paying tax.
These trusts are perfectly above board in New Zealand and there is no evidence that either man has done anything illegal.
Their mistake, it seems, was using Panama law firm Mossack Fonseca to structure their finances. For doing so, the pair are now among scores of politicians and public figures facing scrutiny after 11.5 million records were leaked.
Dubbed the "Panama Papers", the document trove is the largest ever of its kind and is said to reveal how "heads of state, criminals and celebrities" hide their assets offshore.
"The cache of 11.5 million records shows how a global industry of law firms and big banks sells financial secrecy to politicians, fraudsters and drug traffickers as well as billionaires, celebrities and sports stars," says the International Consortium of Investigative Journalists, which spent a year analysing the leaked papers.
While 60,000 of these documents are believed to relate to New Zealand, only a handful have so far been released.
However, the scandal has already seen New Zealand labelled a tax haven and has raised questions about whether the country's foreign trust industry is open to abuse.
Prime Minister John Key has rejected this contention and backed the country's tax regime.
Whether his position remains tenable will likely hinge on the contents of the remaining documents and any further damage they cause New Zealand's good name.
And with United States President Barack Obama calling for international tax reform after the papers were released, Key will also want to appear on the right side of history.
In the uproar this week, Key was forced to defend his vision of modelling this country on Switzerland or Jersey - neither of them known for their financial transparency.
"Is he not concerned that, on his watch, New Zealand is building a reputation as a sunny place for shady people?" Green Party co-leader James Shaw asked in Parliament. Unlike some other world leaders, Key has not been personally embarrassed by the controversy.
Iceland's Prime Minister Sigmundur Davio Gunnlaugsson, on the other hand, was confronted by sweeping protests over revelations that he owned a holding company in the British Virgin Islands.
He resigned on Wednesday.
British Prime Minister David Cameron fended off questions about his family's finances before admitting he benefited from a Panama-based offshore trust set up by his father.
Russian President Vladimir Putin stared down claims that his associates moved up to US$2 billion through "banks and shadow companies" and dismissed the leak as nothing more than a Western smear campaign.
Little known before this week, Mossack Fonseca has now been thrust into the public eye and is described as a "gatekeeper to a vast flow of murky offshore secrets".
"The firm is one of the world's top creators of shell companies, corporate structures that can be used to hide ownership of assets," the ICIJ said on Monday.
"The firm's customers have included Ponzi schemers, drug kingpins, tax evaders and at least one jailed sex offender."
Mossack Fonseca, however, says it is a responsible member of the financial community and has never been accused or charged with criminal wrongdoing.
"For 40 years Mossack Fonseca has operated beyond reproach in our home country and other jurisdictions where we have operations," it said.
One of those jurisdictions is New Zealand, where the firm appears to have a local branch based in the offices of Auckland's Bentleys Chartered Accountants.
Orion Trust (New Zealand), which the ICIJ describes as being linked to both Mizzi and Hinojosa, is also located at this address and directed by Remuera's Roger Thompson and two men from Panama.
Although one of the ICIJ's members called it a "Mossack Fonseca trustee company", Thompson said he could not disclose whether or not that was the case.
"We can't give any specific comment on any specific client which we might act for," he said on Monday.
"As a general comment, we always undertake a rigorous due diligence process with any clients we accept and all tax laws and anti-money laundering laws and all those sorts of things are complied with."
Orion is just one of the local firms that manages more than 11,500 trusts on behalf of foreigners.
The industry generates about $24 million in fees each year, making it something of a minnow in our financial services sector.
While these trusts are the traditional stomping grounds of lawyers and accountants, there are no rules setting out who can and cannot manage one.
Introduced in their present form in 1988, they have long been a facet of New Zealand corporate life. This week is by no means the first time they have courted controversy.
"Our foreign trust rules continue to attract criticism, including claims that New Zealand is now a tax haven in respect of trusts," the IRD said in a 2013 report.
"This is largely because the mismatch between our rules and those of other countries may result in income not being taxed either in New Zealand or offshore. To protect our international reputation, it may be necessary to strengthen our regulatory framework for disclosure and record-keeping," it said.
No such changes have been made.
One of the reasons for the perennial popularity of foreign trusts is that they pay no tax on income earned overseas.
This, unsurprisingly, is also why these trusts can be used to reduce the tax a person would otherwise pay in their home country.
The theory goes something like this.
Assume a Brazilian mining magnate settles $10 million in a New Zealand trust. In turn, these funds are invested in Panama, where little or no tax is paid on the proceeds.
If held in the magnate's own name, it is likely he would be required to pay tax in Brazil, on the basis that residents are usually taxed on their worldwide income.
However, because the investment was made by the New Zealand-based trust, no tax is payable in the South American country.
And because New Zealand does not tax the overseas income of a foreign trust, none is paid here either.
While we know how many of these trusts there are, there are many things we don't know.
One of those unknowns is how much income is earned by these foreign trusts, as this is not information the IRD requires from local trustees.
As well, we don't know the value of the assets held by these trusts, as local trustees are not required to disclose this to our tax authorities.
Nor must they routinely inform the IRD about the identity of the person setting up the trust, or their country of residence.
In fact, the only information trustees must give authorities is their own contact details and the name of the trust they are in charge of.
At first blush, this hardly appears to amount to the "full disclosure" which the Prime Minister claimed surrounded these trusts.
Key, however, elaborated in Parliament on Tuesday, saying trustees must keep detailed financial records. "The Inland Revenue Department can get this kind of information and will give it to the tax authorities in any other country if requested under a relevant tax agreement, or proactively if that country wishes," he said.
"I am advised by the Inland Revenue Department that New Zealand has always been able to comply with these sorts of information requests from treaty partners. This is certainly full disclosure of information."
It is this disclosure which Key relied on to distinguish this country from the likes of Belize and the Seychelles, which were named alongside New Zealand as a "tax haven" used by Mossack Fonseca.
"It is ridiculous to suggest that New Zealand is a tax haven," he said.
But according to University of Auckland tax law specialist Michael Littlewood, New Zealand "plainly" fits his definition of one.
"Every Government in the world denies it is a tax haven," he told the Weekend Herald.
"If you define 'tax haven' in a contrived fashion, it's easy to come up with the conclusion that New Zealand is not a tax haven.
"For practical purposes, the useful definition of 'tax haven' is a country that allows itself to be used by non-residents to avoid the tax they'd otherwise have to pay in their home country. On that definition New Zealand is plainly a tax haven," he said.
New Zealand's treatment of foreign trusts seemed to be the only instance where the country was "right out of step with OECD norms".
"It appears to be the case that New Zealand is the only one that neither taxes the income nor requires any meaningful disclosure," he said.
A "tax haven" was also what New Zealand was called by accountant Geoffrey Taylor, whose GT Group was linked to more than 1000 shell companies in this country.
One of those companies, Auckland-based SP Trading, caused an international scandal in 2009 after it was linked to a plane seized in Thailand carrying 35 tonnes of North Korean weapons.
The incident was one driver of the Government's painfully slow shell company crackdown and the introduction of rules requiring all firms to have at least one local director.
Taylor's son, Ian, would emerge as a player in the Panama Papers this week, linked to thousands of companies identified in the 11 million leaked documents.
Even before this week, the Taylors had long vanished from view and both are believed to live in Australia.
Their brief resurgence, however, serves as a reminder that stains on New Zealand's reputation can linger.
Which leaves one question: is that reputation really worth just $24 million a year?
Q&A
What are the papers?
A huge leak of 11.5 million documents from a Panama law firm, which reveals how the world's rich hide their money.
Where does the leak come from?
Panama-based Mossack Fonseca, one of the world's most secretive offshore law firms. The firm said it had never been charged with criminal wrongdoing.
Who got the papers?
The documents were obtained by Sueddeutsche Zeitung, a daily newspaper headquartered in Munich. Sueddeutsche shared the Panama Papers with the Washington-based International Consortium of Investigative Journalists (ICIJ) and other news outlets, including the BBC and the Guardian. Sueddeutsche said an employee at the law firm had leaked the data, telling the newspaper he risked his life in doing so. The employee was not identified in the report. Some 370 journalists in 78 countries were involved in evaluating the data dump. Sueddeutsche tweeted: "2.6 terabytes of data, 11.5 million documents, and 214,000 shell companies: The Panama Papers are the largest data leak journalists have ever worked with".
What do they show?
The documents link at least 12 current and former heads of state and 128 other politicians to illicit financial transactions.
What about NZ?
The papers show a Mexican tycoon and Maltese politician have established trusts in New Zealand. The ICIJ, in its coverage, has also labelled New Zealand as a tax haven - alongside 21 other jurisdictions including the Seychelles, Panama, Samoa, Niue, British Anguilla, British Virgin Islands, Jersey and the United Kingdom.
What happens next?
More revelations are expected from the papers, particularly if the ICIJ releases the full trove of documents next month. Inland Revenue also says it is trying to get information on New Zealanders who have dealt with Mossack Fonseca. "We are working closely with our tax treaty partners to obtain full details of any New Zealand tax residents who may have been involved in arrangements facilitated by Mossack Fonseca," said IRD international revenue strategy manager John Nash.
