No charges will be laid over the alleged theft of a journalist's recorder at a Labor state conference in 2014, Victoria's Office of Public Prosecutions (OPP) has recommended.

ALP members allegedly stole Fairfax journalist Farrah Tomazin's dictaphone from the lost property box at the May conference after she dropped it.

Details of a recording of former premier Ted Baillieu criticising some of his party colleagues were then emailed to Liberal Party members.

Police investigated the matter but the OPP said no charges would be laid.

"The Office of Public Prosecutions this week provided advice to Victoria Police regarding the alleged theft and destruction of a dictaphone in June last year," Victoria Police said in a statement.

"Their recommendation is that no charges be laid in relation to this matter."

Senior Labor Party figures admitted they listened to the tape in July last year.

Victorian Labor's assistant secretary Kosmos Samaras said in July that he destroyed the recording device after listening to its contents and hearing a conversation with himself and other senior politicians.

"I listened through the device to ascertain whether there were any other recordings of my private conversations," Mr Samaras said in the statement.

"In doing so I listened to numerous senior politicians on both sides of politics and others whose private conversations which I presumed had also been recorded without their knowledge.

"After some consideration, I decided that given the device contained unauthorised private conversations, it was not appropriate to retain, return or disseminate the device. I destroyed it.

"In hindsight, this was the wrong thing to do. I should have returned the device and sought an explanation for why I was being recorded. I apologise to Ms Tomazin and the Age for not having returned the device."

The Age editor 'surprised' by OPP decision

Editor-in-chief of the The Age newspaper Andrew Holden said he was "a bit surprised" by the OPP's decision.

"I would've thought it was a clear case when Mr Samaras himself has admitted that he had possession of the tape recorder, he listened to it, he downloaded a copy of the interviews ... he played it to a number of people and then he destroyed the dictaphone," Mr Holden said.

"All of them as far as I can tell from my reading on the law are in clear breach of the act, so I'm a little bit surprised that there's no consequences - or appear to be no consequences - for him."

Mr Holden said The Age had accepted its failure to protect the private conversations on the tape recorder and that the OPP decision was disappointing for Ms Tomazin.

"At the end of the day Farrah [Tomazin] was the victim here, it was her dictaphone that was stolen and was listened to and then was misused," he said.

"It's a shame for her given the amount of probing that was thrown at her that she appears to be the only one who's copped some consequences out of this and those who were behind what happened to that tape recorder are not."

He said the paper "remained curious" how the recordings got from the ALP state office to the Liberal Party.

"There are still some significant questions to be answered as to who else got hold of the tape recording, particularly the Baillieu recording, why they released those in such a public way, and I think that matter continues," Mr Holden said.

Labor says OPP decision 'ends the matter'

The Acting Premier, James Merlino, said the decision not to lay charges marked the end of the matter for Labor.

"We've always said that the authorities have had a job to do and they've done that," Mr Merlino said.

"From my perspective that's the end of the matter."

In July last year, Victorian Premier Daniel Andrews, who was Labor's opposition leader at the time, said he had no involvement in the matter and did not know how the contents came to be leaked to Liberal MPs.

However Labor state secretary Noah Carroll said he and Mr Andrews's chief of staff John McLindon listened to one of the recordings with Mr Samaras.

"Mr McLindon, Mr Samaras and myself listened to one of the files and we were informed by Mr Samaras that there were many more like them," Mr Carroll said in a statement at the time.

"It was collectively agreed later that same day that all of the contents should and could not be circulated further in any way. Subsequent to this, all files from the device were destroyed."