An admissibility ruling by a judge in the trial of two former soldiers accused of a Troubles murder has triggered a chain of events that has led to the halting of two further legacy cases in Northern Ireland, including the only prosecution ever mounted over the notorious Bloody Sunday killings of 1972.
Here is an explanation of why the controversial prosecutions have unravelled.
What happened in the Joe McCann murder trial?
Soldiers A and C, both former paratroopers, went on trial in April accused of murdering the 24-year-old Official IRA leader who was shot dead by soldiers as he attempted to evade arrest by a plain-clothed police officer in the Markets area of Belfast in April 1972.
The trial before Mr Justice O'Hara opened at Belfast Crown Court and heard a full day of evidence. It then moved into a separate voir dire hearing to determine whether statements and interviews given by the ex-soldiers, who are now in their 70s, would be admissible as evidence.
The voir dire heard that the evidence implicating the defendants came from two sources. The first was statements they made to the Royal Military Police in 1972 and the second was statements and interview answers they gave to a police legacy unit, the Historical Enquiries Team (HET), in 2010.
In an unequivocal ruling, Mr Justice O'Hara found none of the evidence should be admitted to the trial, highlighting a series of deficiencies in the reliability of both the RMP and HET material.
With the Crown case hinging on the evidence no longer admissible at trial, the Public Prosecution Service (PPS) could not proceed without it. Having determined there were insufficient grounds to appeal against the judge's ruling, prosecutors formally offered no further evidence and the soldiers were duly acquitted.
Why was the RMP evidence ruled unreliable?
This was due to a series of failings in the RMP process. The controversial practice of the military investigating its own actions in Northern Ireland was discontinued in 1973 amid concerns it was designed to ensure soldiers were protected from questioning by police so they could avoid prosecution.
Judge O'Hara branded the RMP procedure an "appalling practice" that denied the soldiers a series of basic legal safeguards. They were not interviewed under caution, they were not given access to legal representation, they were compelled to make the statements and the soldiers were not given an opportunity to explain why they had taken the actions they did. The circumstances amounted to "oppression", rendering any confession made as unreliable in a court of law.
What about the HET evidence?
The PPS accepted the inadmissibility of the RMP statements, in isolation, from the outset. However, prosecutors argued the information in the 1972 statements became admissible because they were adopted and accepted by the defendants during their engagement with the HET in March 2010.
Justice O'Hara not only dismissed that contention, claiming it was not tenable to put the 1972 evidence before the court "dressed up and freshened up with a new 2010 cover", but he also raised concerns about the HET process itself.
He questioned whether the HET's role was to conduct criminal probes or to fact-find to bring resolution and answers for bereaved families.
As such, the judge said there was ambiguity as to why former soldiers were being asked to participate in the process. Justice O'Hara said if evidence of criminal wrongdoing emerged in the HET process that should have been subjected to a formal investigation by the Police Service of Northern Ireland, rather than being used as a basis to mount a prosecution. He noted that when Soldiers A and C were interviewed under caution by the HET, neither veteran was informed what criminal offence they were suspected of before they faced questions.
Why does the judgment affect the prosecutions against Soldier F and Soldier B?
While not exactly the same, the evidence against the former soldiers was of a similar nature to that ruled inadmissible in the Joe McCann trial. Following receipt of Justice O'Hara's detailed written judgment, the PPS initiated formal reviews of the cases. The PPS is under an ongoing obligation to keep prosecutorial decisions under review to account for changing circumstances.
Soldier F/Bloody Sunday:
While the PPS has long acknowledged that free-standing RMP statements given by soldiers could not be used in evidence against them, in the Bloody Sunday case, the PPS was attempting to use RMP statements given by other soldiers in the Bogside that day. They were going to try to use the accounts of Soldiers H and G as hearsay evidence that Soldier F was in the area and had fired shots at the civil rights demonstrators. They believed the issues around oppression were not as compelling when dealing with statements that were not considered direct confessions to criminality.
They were going to ask the court to rely on the aspects of Soldiers H and G's statements that claimed Soldier F was firing in Glenfada Park North when the victims were shot. Without that evidence, the PPS had no way of proving that basic, but absolutely crucial, fact.
Soldier B/Daniel Hegarty:
A pivotal piece of evidence in this case related to a statement Soldier B gave to the HET in 2006. In it, he admitted to firing the shots that hit Daniel and his cousin Christopher. He had also given a statement to the RMP in 1972, but prosecutors accepted that would have been inadmissible.
The 2006 HET statement was therefore the only evidence that could be used to identify Soldier B as the person who fired the shots. The PPS review concluded that deficiencies identified by Justice O'Hara in relation to the HET evidence in the Joe McCann case were also relevant to the 2006 statement in the Hagerty case.
With the prospect of that being ruled inadmissible as well, the Crown case against Soldier B fell away.
Is there any prospect of these decisions being revisited?
The families can attempt to challenge the PPS decisions by way of judicial review in the High Court.
The family of Daniel Hegarty successfully challenged a previous non-prosecution decision against Soldier B. On Friday, a lawyer for the Hegarty family called on the police to obtain a fresh statement from Soldier B - something they said could enable the prosecution to continue.
The McKinney family made clear on Friday that they would be pursuing judicial review proceedings.
The Wray family indicated that they would not be taking further legal action, but would support other families who pursue that avenue.
The families of other victims of Bloody Sunday are currently taking action against the PPS for its decision to not mount prosecutions over the killings of their loved ones.
What about other legacy cases against former soldiers?
The Bloody Sunday and Daniel Hegarty cases are two of seven currently within Northern Ireland's criminal justice system.
In four of the cases, decisions to prosecute had already been taken, while prosecutors are assessing the evidence in the other three cases ahead of issuing prosecutorial decisions. All seven have been looked at again following the O'Hara ruling. Formal reviews were deemed necessary in the Soldier F and Soldier B cases - an exercise that led to the decisions to halt the proceedings.
It was quickly established that the other two live prosecutions do not rely on the type of evidence deemed inadmissible in the Joe McCann case and those prosecutions are therefore proceeding.
Those are the cases of Dennis Hutchings, who is accused of the attempted murder of John Pat Cunningham in Co Tyrone in 1974, and David Jonathan Holden, who is accused of manslaughter by gross negligence in relation to the 1988 shooting of Aidan McAnespie at a checkpoint close to the Irish border.
The other three cases - two involving the Army's Military Reaction Force and the other a fatal shooting at a Cookstown hotel in 1980 - remain under consideration, with prosecutorial decisions not understood to be imminent. The findings of Judge O'Hara will be factored into those deliberations as prosecutors consider whether the test of prosecution has been met in each.