Prime Minister John Key said the MP for Pakuranga had "crossed the line", despite assuring him he did not intend to influence the prosecution.
One of the documents Internal Affairs released yesterday - after previously refusing to do so - was the email Mr Williamson sent to Nathan Guy, the Internal Affairs Minister at the time, to lobby on Liu's behalf.
The department had recommended that the citizenship application be declined on the grounds that the Chinese national did not spend enough time in New Zealand or meet the English-language criteria.
Mr Williamson sent the email to Mr Guy on November 9, 2010, and suggested that the "case be processed as fast as possible".
Mr Guy used his ministerial prerogative and granted Liu citizenship on December 16, 2010.
The following day, Mr Williamson conducted the VIP ceremony himself.
"The department was not advised as to where the ceremony was held, but understands there was a preference for the ceremony to be held at the Office of Hon Maurice Williamson," a spokesman said yesterday.
Most citizenship ceremonies are conducted in public, often with hundreds of others taking the oath of allegiance, so the Liu ceremony raises more questions of special treatment for the businessman.
At a press conference following his resignation yesterday, Mr Williamson said he was not friends with Liu.
"It is pretty hard to have a friend that you cannot speak a word of their language and they of yours ... I don't socialise with him."
Mr Williamson's resignation was sparked by a Herald request under the Official Information Act. The police declined this week to give the Herald the information sought, on the grounds of privacy and the maintenance of the law. But they alerted the Prime Minister's office to our request, in accordance with the Government's "no surprises" policy.
After the Herald broke the story online yesterday, the police released some internal emails because staff had "reassessed" the request and considered the public interest outweighed the other reasons.
The emails showed that Mr Williamson rang Superintendent John Tims, the district commander for Counties Manukau, about the family violence allegation again Liu. Mr Tims referred the inquiry to his Auckland counterpart, Superintendent Mike Clement, on January 20. Mr Clement tasked Inspector Gary Davey to follow up the request and "determine how we respond to MP Williamson". A week later, Mr Davey rang the MP.
"He [Mr Williamson] started by saying that in no way was he looking to interfere with the process," Mr Davey reported back to his superiors. "He just wanted to make sure somebody had reviewed the matter to ensure we were on solid ground as Mr Liu is investing a lot of money in New Zealand.
Mr Davey said he told Mr Williamson the criminal case was reviewed by the senior sergeant in charge of family violence cases, as well as the police prosecution team.
"I told him it was ultimately up to Prosecutions to decide whether they would continue with the case."
In the emails Mr Davey said he told the MP the police would carry on with the prosecution. "I also explained the wider responsibility of police to pursue these matters [redacted]. I told Mr Williamson that the best advice he can give Mr Liu is to have him seek good legal advice. The conversation was polite and professional on both sides and he appeared to be accepting of the police position.
"I will leave the matter there unless I hear otherwise."
Liu's lawyer, Todd Simmonds, told the Herald yesterday his client did not ask Mr Williamson to contact the police on his behalf.
Liu was arrested after a domestic violence incident against his de facto partner and her mother at his Boulevard Hotel, Newmarket, in December. He has since pleaded guilty to assaulting a woman and assault with intent to injure. He is seeking a discharge without conviction.
Others who supported Liu's bid for citizenship included John Banks, then Mayor of Auckland.
Mr Guy granted him citizenship because of the "potential benefits" of his investment in New Zealand.
But the
Herald
has previously revealed he is yet to start a proposed $70 million property development in Newmarket.
The 2010 Liu case was one of several that worried Internal Affairs staff, who raised the possibility of favouritism with the Office of the Auditor-General during an inquiry into a citizenship decision made by Shane Jones when he was a Labour Party minister.
Mr Jones was criticised in the report last year but cleared of any corruption over his decision to grant citizenship to a wealthy businessman who had strong links to Labour.
The Auditor-General was also told of other citizenship files involving support from MPs. An in-depth investigation of those files was beyond the scope of the original inquiry but nothing was found to suggest that decisions were made "as a result of improper influence".
"However, it is clear that the apparent links between different applicants and their agents, or supporters, coupled with strong support from various MPs and subsequent questions from the minister or ministerial officials caused disquiet among some citizenship officers," according to the inquiry report.
The Auditor-General said there was nothing wrong or improper with MPs advocating on behalf of constituents in citizenship cases, or ministers considering those representations.
"However, advocacy of this kind, in particular where the advocate is a fellow MP or known to the minister, clearly presents risks to the integrity of the decision-making system and to the reputations of those involved," the Auditor-General wrote.
Liu opened the $3.5 million refurbishment of the Boulevard Hotel with Mr Key and Mr Williamson in time for the Rugby World Cup as the first stage of an ambitious project to rejuvenate the derelict site.
Nearly three years later, the four-star hotel is now a $400-a-week accommodation lodge and 20,000sq m of prime land behind it lies empty, with no resource consent applications lodged for the proposed hotel, apartment blocks and shops.
The proposed $70 million project at the former Carlton Bowling Club site stalled after Liu unsuccessfully lobbied the Government - again with support from Mr Williamson - to relax business immigration rules for wealthy foreigners.
Liu hired professional consultants Exceltium, led by Matthew Hooton, to lobby the Government to lower the $10 million threshold that non-English-speaking applicants need to invest to qualify as business migrants. He said his plan was unlikely to go beyond the design stage unless the rules were changed to source capital from overseas, particularly China. A policy change to relax the rules is still under consideration by the Immigration Minister.
