Those who investigate the dark aftermath of conflict walk on dangerous ground. The murder by dissident republicans of Lyra McKee in April was a chilling reminder that there are paramilitaries who are still intent on dragging us back into the hostilities of the past. Another case that has been playing out in Northern Ireland’s legal system is a shocking warning that this may also be true of the police.

Treatment of Northern Irish journalists likened to police state, court hears Read more

This case yielded a great victory for press freedom in Belfast’s high court last Friday, but the two brave investigative journalists who brought it about are still caught in a nightmare worthy of Kafka. They remain on police bail, facing unspecified criminal charges. This despite the fact that the highest judge in the Northern Irish state, the lord chief justice, has declared that on the basis of the evidence put before him, they have done nothing wrong.

The pair, Barry McCaffrey and Trevor Birney, were arrested last summer for their work on a documentary about a 1994 massacre. The reason? We learned in court last week that a senior police officer was concerned that their investigation might have put lives in danger. If there were any evidence for this, and there is none, it might sound reasonable enough. But it also turns out the lives the police were concerned about were those of people “having the misfortune of being involved in terrorist atrocities”.

The misfortune? Even by Northern Irish standards this was, as a barrister representing the journalists put it, “a staggering proposition”. Durham constabulary, brought in by the Police Service of Northern Ireland (PSNI) to investigate, had, said Barry Macdonald QC, conducted “the kind of operation associated with a police state rather than a liberal democracy”.

Facebook Twitter Pinterest Journalists Trevor Birney and Barry McCaffrey outside the Royal Courts of Justice, Belfast, on 31 May. Photograph: Brian Lawless/PA

In a few weeks it will be 25 years since the Loughinisland massacre, when a loyalist gang burst into a quiet rural pub in County Down and opened fire. Six men were killed. They had been watching a World Cup match between Ireland and Italy, their backs to the door. Five more were injured. One of them, the barman, Aidan O’Toole, says he relives those events constantly, to the point that he sometimes wonders if he was lucky to survive.

With the blood of the dead still wet on the ground in Loughinisland, the then secretary of state for Northern Ireland, Patrick Mayhew visited the scene and repeated the police vow that the authorities would “leave no stone unturned” in pursuing the killers.

But it was not long before the bereaved families began to feel that there was something not quite right about the investigation – that, in fact, it did not appear to take place at all. No one was ever tried. A review by the police ombudsman in 2016 found there had been “catastrophic failings” and that the police had colluded with the killers, believed to be members of the illegal loyalist paramilitary group the UVF. The time was obviously right for a serious documentary.

Facebook Twitter Pinterest Trailer for Alex Gibney’s documentary No Stone Unturned.

McCaffrey, who had been investigating and reporting on the atrocity for years, and Birney, who had set up a film company specifically to explore such difficult stories, were the obvious journalists to take it on. Birney brought in the Oscar-winning director Alex Gibney and the 2017 film they made, whose title, No Stone Unturned, brilliantly upends Mayhew’s promise, pursued the evidence the police ignored and went so far as to name the alleged murderers. The journalists informed the police of their intention to do so months before the film premiered. Surely, it was up to the police to assess if there was any potential threat to lives, and to advise the film-makers accordingly. It appears they did not.

The chief constable of the PSNI, George Hamilton, had accepted the findings about collusion in the 2016 ombudsman’s report. The documentary consolidated its findings. The time was more than ripe for the police to finally investigate the killings.

After the film premiered, police did, in fact, visit the home of the person accused in it of being the gunman. But unbelievably, they did so not to question him about the murders, but to ask him how the film had affected him, and what he thought about the police ombudsman. He told them he was living in fear and his vermin-control business was in ruins. He was asked who he blamed and he said it was the film-makers and the ombudsman.

And so it was that police arrived on the doorsteps of the two journalists one morning. They were arrested and taken into custody. Police seized computers and files containing the equivalent of millions of pages of journalistic material, only a tiny proportion of which related to No Stone Unturned. The lord chief justice commented in court last week that it was unclear what crime the police thought they were investigating. The police’s barrister spoke darkly of the Official Secrets Act and the need to protect informants. They were investigating the theft of a document from the police ombudsman’s office, he said – even though the ombudsman has denied reporting any such theft. The film did make use of a leaked document from an anonymous source. But the journalists had been entirely candid about this.

Facebook Twitter Pinterest The funerals of two of the Loughinisland victims, Barney Green and his nephew Dan McCreanor. Photograph: John Giles/PA

The police acted as though they were unaware that journalists and the whistleblowers who provided the public with information that is in the public interest were protected both by UK law and by the European Convention on Human Rights.

In the event, the lord chief justice declared the arrests “inappropriate”. Birney and McCaffrey had behaved properly, Declan Morgan found. The work of journalists was essential in holding the state to account, “particularly in a society like ours where confidence in the institutions is so important”, he added. The police had not behaved properly he found, ordering them to return the material they had seized.

Investigating the Loughinisland murders – podcast Read more

This ruling was a landmark victory for investigative journalism. However, the apparent determination of the police to pursue the criminal prosecution of the journalists is scandalous. It is also a further insult to the Loughinisland victims’ families. Patrick McCreanor, who lost his uncle and great-uncle in the massacre, said the families want the police to change course now, and pursue the killers. If they refuse, we will know where we stand in Northern Ireland. Not in the democracy promised by the Good Friday agreement, but in a police state.

• Susan McKay is an Irish writer and journalist