Hager wrote how Whaleoil blogger Cameron Slater conspired with a staff member in the Prime Minister's office, Jason Ede, to access Labour Party information through a hole in its website. He reported how Ede had avoided being identified by using a "dynamic IP address" which meant efforts to track him failed.
The details revealed in the book led to the Labour Party complaining it had been hacked, among other claims. The other matters were dismissed by police last year. The reason, in a letter from Mr Drew, was that the "only evidence being relied on was contents of Mr Hagar's (sic) book and the entities and persons named did not want to pursue any action".
The letter from Mr Drew spelled Mr Hager's name wrong and the name of the Labour Party general secretary Tim Barnett.
Mr Barnett - "Barnnet", according to police - said the police conclusions were "unbelievable". He said the party was considering further action.
He said the effort being put into investigating Slater did not compare to the greater energy put into investigating Hager.
"I would expect to see a level of energy from the police that was equitable and we certainly haven't seen that in the treatment of us."
Two government inquiries into matters raised in Dirty Politics found evidence given by Slater could not be relied on - and that he had overstated his contacts and influence.
Hager is awaiting a High Court judgment on whether he can claim journalistic source protection in relation to the anonymous individual known as Rawshark who claimed to have hacked material from Slater's computer system. It followed a complaint by Slater and a police raid on Hager's house searching for information leading to the hacker's identity.
Police had previously dismissed a complaint by Matthew Blomfield that Slater had illegally accessed a computer hard drive to get emails and personal information used for blogposts. Blomfield has since taken defamation action against Slater over the posts.
Ongoing fallout from Dirty Politics saw The Standard website recently lay a complaint with police alleging Slater had attempted to hire a hacker to access the left-wing blog.
Slater, who has denied any wrongdoing, said he would be seeking an apology from Andrew Little over the accusations.
• An original version of this article stated that Cameron Slater did not wish to comment. In fact, Mr Slater had asked to see a copy of the police correspondence before considering a response. His comment in this article is from his blog.
