The problem as I understand it was that the National party tech and Slater (the two who could be identified from the logs) said that they hadn’t taken or tampered with anything. They had merely “looked” at what was there.
Since that involved copying information and would have shown up on the logs, that is probably still illegal as there is a copy taken. However that is “
actus reus“, the guilty act. Often to prove criminality you have to prove criminal intent “
mens rea“, the guilty mind. The latter wasn’t clear in 2011 and would have been difficult to prove. So the NZLP dropped it as being potentially too embarrassing in an election year.
However the conversations revealed in “Dirty Tricks” clearly show that there was a guilty mind. Slater, Bhatanger, and Ede were clearly intent on being malicious – in particular in stating that they would hold and use the files that they obtained to attack the Labour party and its contributors.
That the evidence that proved this was also obtained illegally is unlikely to have any particular bearing on the use to lay criminal charges or to convict.