Prime Minister John Key believes former National leader Don Brash's emails were hacked, not leaked, but the mystery will probably remain unsolved now that police have closed the file after a review of the investigation. "I think the computer system was hacked into. That's my view, but I can't back that up," Key said yesterday. He had his own theory on who did it, but would not name anyone. "This is not Agatha Christie's whodunit. I just don't know." He rejected suggestions the leaks came from disgruntled National Party insiders. "That's a great sort of nonsense, sort of fiction put out by the Left. `Bollocks' is another way of putting it, if you want." Brash resigned as National Party leader in 2006 after the publication of the book The Hollow Men by researcher Nicky Hager and after details of his private life were aired in public. The book was based on emails and other material sent to and from several political insiders including Dr Brash. A police review of the investigation, made public yesterday, has again failed to establish the source of the leaks but found the inquiry was conducted properly. Hager rejected Key's theory. He has consistently said the emails were leaked. "If anyone doesn't believe the police now, well, they're cranky and not to be taken seriously." He said it was incredibly undignified that Key had come up with such a wacky idea that the emails had been hacked. "Anybody who understands computers and things like hacking will know it is completely impossible. For John Key to be raising that now is really surprising. He's obviously not taking an evidence-based approach ... because there is no grounds for that." Hager said he had been interviewed once by the police and had been "very helpful". He could not tell them his sources, though he eliminated some possibilities. The review, led by Auckland Region Assistant Commissioner Steve Shortland, was prompted by complaints by Brash that the investigation was conducted in a "cavalier fashion" and was politically biased. The review found that the investigation was competently carried out, but it criticised the lack of timeliness of progress reports and the delay before Brash was given the final report. There had also been a lack of "urgency" once it found there was no threat to national and parliamentary security. There was no evidence of political bias. Police, though, were now developing new guidelines for handling politically sensitive allegations. The review had found unsatisfactory security on Parliament's third floor, where Brash's Opposition leader offices were. Hacking of the parliamentary server was highly unlikely. There was no evidence to suggest Hager had committed any crime. "I am fully satisfied that everything possible has been done to identify the source of the emails and this is now the end of the matter," Shortland said. Key said he was not worried about his own email security "because I am not in the process of sending dodgy emails". But it was always possible someone could break in. He said other people such as contractors had access to those systems. Brash said the culprit would probably never be identified, and he regretted that. But he was pleased police had interviewed all potential suspects, some for the first time. "Even though their inquiries have failed to identify the source of the leak, I certainly appreciate the effort they have put into this second investigation."