An extradition request was part of a reciprocal treaty and not out of order - but it was nevertheless delicate and conducted at the highest levels, he said.
"It's not done at the local level. It's most likely that the Secretary of State - Hillary Clinton - personally signs it.
"Between the FBI and Hillary Clinton, it goes past a thousand eyes because they're asking a sovereign country to put somebody on a plane."
The final request would have to be robust, Mr Tan said.
"You're not going to give Hillary Clinton a bunch of dud papers to sign, because it makes her look silly."
Dotcom is in custody as he awaits a February 22 callover, having had requests for bail declined.
His heavily pregnant wife - who has been described as in a "frail" condition - is living at their house in Auckland with their three children.
Most of the family's possessions have been seized by authorities.
The indictments for Dotcom and his co-defendants have been made available, but the official extradition request is yet to be lodged.
The deadline is March 5.
Mr Tan said the money-laundering and racketeering charges had been devised on the back of the alleged copyright infringements.
Money-laundering charges applied to any transactions of money made from serious crime - even where there was no attempt to conceal it, he said.
"A guy hits a grandmother over the head and steals her handbag for $30, then buys a pack of cigarettes with it - if you deal with it in any way at all it becomes money laundering," he said, though he added that the original crime must be serious, usually carrying a jail term of at least five years.
As part of the charge, the indictment against Megaupload lists a series of payments to the firm hosting its servers.
Elsewhere in the document, the prosecutors allege that the website concealed its criminal activity because it withheld copyrighted files from its search results.
Mr Tan said the racketeering charge could be applied where a group of defendants faced two crimes out of a list of 35, which included copyright infringement and money laundering.
The charge had been "extremely successful" in elevating penalties and dealing to organised crime and the Mafia.
There was no direct equivalent to the charge in New Zealand, Mr Tan said, although various fraud charges could add up to something similar.