After four months of illegal police surveillance on a closed Facebook page, Rhys Liam Halvey was arrested and charged with three counts of using a carriage service to offend police and a further three counts of publishing an indecent article.

The surveillance tactics were later supported in court by one of the highest ranking police officers in the state.

The "indecent" posts included a raunchy image of the American pop star Miley Cyrus that had been superimposed on a photograph of a serving officer. After Sydney magistrate Roger Brown warned that a "criminal offence" had been committed by the "unauthorised access", a senior member of the NSW Police hierarchy attempted to intervene with two sworn affidavits "supportive" of the actions.

But all six charges have now been withdrawn and dismissed. In ordering costs against police, Magistrate Brown described the conduct as "reprehensible" and the charges as "trivial."

"Exactly how widespread is this snooping?" asked Mr Halvey's barrister, Andrea Turner, in a formal complaint to the Police Integrity Commission, which has now been referred back to the police, by the NSW Ombudsman, for investigation.

"There is no difference to the police trespassing on a Facebook page for four months and my steaming open my neighbour's mail in the hope of one day finding something, anything, to report to police."

NSW Council of Civil Liberties president Stephen Blanks said public confidence in the police was being "undermined" by an inability to acknowledge the occasions when "it does the wrong thing."

"How deep in police culture is this willingness to break the law?" he asked. "Even after they have been caught out, it would appear no adverse consequences are going to be suffered by those responsible because the illegal actions are supported by police at the most senior level."

On November 29, 2013, NSW Police Senior Constable Daniel Moss began spying on a closed Facebook page belonging to a "Rhys Brown" using someone else's user name and password. The prying continued until March 31 last year, when several "derogatory" posts appeared.  They featured a NSW Police infringement notice together with photographs of several serving officers, taken in a Sydney street setting.

One image carried a large sum of cash and words to the effect of: "Here's my $25,000 for your $101 fine." Another image depicted Miley Cyrus "twerking" in front of an officer.

Though he denied being Rhys Brown and the owner of the posts, Mr Halvey was charged. During a hearing in April, Magistrate Brown said to Constable Moss: "You use the term 'monitored' the Facebook account of Rhys Brown ... you went into that account frequently?"

"Yes, I did" replied the officer.

"So ... you didn't obtain a Supreme Court warrant ... you didn't obtain any judicial authorisation to invade the privacy of Rhys Brown's Facebook, did you?"

"No."

It was under cross examination that he admitted to using someone else's user name and password.

When the police prosecutor sought an adjournment so the Crown could argue the "public immunity aspect" of certain police "methodology" used to "access data", Mr Brown said: "Police methodology doesn't permit the police to commit crimes, it's as simple as that."

Several weeks later, a senior police official stepped in with with one "confidential" affidavit and another open  in which he relayed previous support for the investigation. He also requested the officer be excused from further cross examination "about how certain Facebook posts were obtained", adding it would be "injurious" to the public interest if "those questions were to be answered".

Mr Brown rejected the immunity application. In September, the case was withdrawn and dismissed with $14,429 in costs ordered against the police.  A NSW Police spokesman said on Friday an investigation was "currently running."