Operation Elveden: The investigation into 'chequebook journalism'
It cost £15m and took five years but what did Operation Elveden - the police investigation into inappropriate payments to police and public officials by journalists - aim to achieve?
Given that it has been repeatedly criticised by the country's biggest newspapers, it is ironic that it was initially sparked by, in effect, the press handing itself into the police.
In 2011, the British arm of Rupert Murdoch's News Corporation passed on to Scotland Yard a thick file of emails revealing that police and prison officers, soldiers and Ministry of Defence officials - as well as their friends and relatives - had been paid thousands of pounds for stories.
Despite the fact that some of the payments were covertly funnelled through branches of the travel agent Thomas Cook, it wasn't a particularly secret practice.
Cash for copy was and still is a core part of the business model of some newspapers, in particular the Sun. Mr Murdoch was later caught on tape telling his journalists they hadn't done anything that wasn't part of the tabloid culture.
But all of a sudden it seemed it could be illegal.
As part of Operation Elveden there were dawn raids, suspects' homes searched in front of their families, 90 arrests were made. There was fury at the treatment of journalists, who often claimed they had acted in the public interest.
The charges were of misconduct in public office, yet the journalists weren't public officials. They were dragged in as co-conspirators for making the payments.
When the cases came to court the view of juries was clear - they convicted the public officials but allowed most of the journalists to walk free, while others successfully appealed.
Different test for press
In a 2015 Appeal Court judgement, the law appeared to catch up. Judges concluded corrupt police officers and prison staff taking money for information could still expect prosecution, but for journalists there should be a different test.
Prosecutors said if there was no harm to the public interest, it might not be in the public interest to prosecute. It was not a get out of jail free card, but a reinforcement of the principle that journalists might be able to pay a whistleblower to reveal a story which the public would welcome being told. Another MP's expenses scandal for example.
Some harm was done by the payments to public officials.
The stories included details of servicemen and women being killed in action, which were leaked before they were officially made public. This premature publication distressed families.
One MoD official, Bettina Jordan-Barber - who was well-placed to sell information - made £100,000.
But the complexity of the inquiry also meant journalists under suspicion had to endure months of uncertainty about whether they would be prosecuted.
Could the police have ignored the evidence they were given in 2011?
It would have been difficult, since the prevailing narrative at the time was that the Met in particular was too close to its friends on national newspapers.
Scotland Yard stresses it had no choice but to act when faced with evidence of corruption, not least involving nine police officers.
Its £15m investigation has secured 34 convictions, but it has also secured a little more certainty about where the law draws a line when it comes to the murky practice of chequebook journalism.