Police officers who raided the mansion of internet magnate Kim Dotcom put together a list of belongings for United States authorities to seize.
The FBI used the list to get a new restraining order from US courts allowing them to seize belongings they never knew existed.
It included diamond-encrusted jewellery from the bedroom of Dotcom's wife, Mona, and a collection of designer watches valued from $10,000 up.
The Government is coming under scrutiny over its actions in the year before Dotcom and three others were arrested in January on US charges of criminal copyright violation and money-laundering.
The FBI-led case led to raids across the world and the closure of Dotcom's file-sharing business, Megaupload, which had claimed to carry 4 per cent of the world's internet traffic.
Dotcom's legal team has signalled it might sue the New Zealand Government over its response to the US request and the way it carried out the raid.
The first restraining order listed Dotcom's exotic and luxury fleet of cars, the statue of the Predator from the Hollywood movie and a string of belongings identified by monitoring email accounts of the accused men.
But a police headquarters spokesman said officers were asked by the FBI to discover the extent of Dotcom's wealth.
He said the request to "establish Mr Dotcom's and his co-defendants' asset holdings in New Zealand" was honoured up to and beyond the January 20 raid.
Each article found was detailed for the FBI, which got a new legal order on January 25 to seize the rest of Dotcom's property on the basis it was bought with "tainted" money.
Police have confirmed to the Herald they received an initial request for help in March 2011.
Through the Official Information Act, it has emerged the Government's lawyers at the Crown Law Office began working on the case in July 2011.
Prime Minister John Key carried out a lengthy television interview last Friday to deny any knowledge of Dotcom until the day before the raids even though his senior ministers, a string of senior civil servants and his own electorate staff were involved in matters relating to him.
It has emerged that staff in the Prime Minister's own department were aware of Dotcom and his bid through the Overseas Investment Office to buy the mansion in which he lived with his family.
The purchase was approved by Overseas Investment Office officials and Land Information Minister Maurice Williamson in April 2011.
But Justice Minister Simon Power declined his application to buy the mansion in July.
A spokeswoman for the Prime Minister said: "The Prime Minister's office was briefed by Hon Power's officeof the minister's decision as acourtesy.
"The briefing was a brief phone call between two staff members - one from Hon Power's office and one from the Prime Minister's."
She said Mr Key was not told any details of the briefing.