An investigation into the theft had closed, Wellington police district crime services manager Detective Inspector Harry Quinn said.
It had not identified those responsible.
“How the thefts occurred still largely remains a mystery,” Mr Quinn said.
“We have eliminated the suggestion that an external ‘computer hacker’ had breached the computer security within Parliament, but there remains many other potential ways in which the crimes could have occurred.”
The investigation established that emails created between October 2003 and November 2005 had been stolen from the ownership of Dr Brash, but found no evidence of thefts since November 2005.
Mr Quinn would not speculate on how he thought the emails had been taken from Dr Brash.
“There are strong indications that the emails were in printed form at the time of the theft, but with the thefts perhaps happening at any time over the two-year period it is very likely that they were stolen during several incidents,” he said.
Police interviewed parliamentary computer staff, parliamentary security staff, cleaners, Dr Brash’s staff, politicians, journalists and friends of Dr Brash.
“Many of them had their own theories on who was responsible and why the thefts had occurred,” said Mr Quinn.
“But in the end no firm evidence pointing to a potential perpetrator was uncovered. The file is closed until someone comes forward with some compelling evidence.”
Interesting that they think printed e-mails were stolen, rather than an electronic copy. If so then that is beyond doubt a criminal act.