A judge has reserved his ruling on whether statements made by two former paratroopers accused of murdering an Official IRA leader in 1972 can be admitted as evidence in their trial.

Mr Justice O’Hara was told by a Crown lawyer on Thursday that his determination would be pivotal to the prosecution case against soldiers A and C proceeding.

During a discrete hearing on the admissibility issue, the judge also described as “remarkable” the fact the ex-soldiers had been prosecuted for Joe McCann’s murder on the basis of a report by a police legacy unit, the Historical Enquiries Team (HET), and not as a result of a follow-up criminal investigation by the Police Service of Northern Ireland.

“One of the remarkable features of the case is after the HET interviews they weren’t interviewed by the PSNI, they weren’t arrested, but they are in court on trial for murder,” he said.

The prosecution was taken after Northern Ireland’s Attorney General referred the case to the Director of Public Prosecutions in 2014 after receiving the findings of the HET re-examination of the case.

Mr McCann, 24, was shot dead as he ran away from police and Army on Joy Street in Belfast in April 1972.

During Thursday’s hearing in Belfast Crown Court, it emerged that the prosecution had conceded that witness statements made by the accused veterans to the Royal Military Police in the immediate aftermath of the fatal shooting would be inadmissible as evidence if considered in isolation.

That is due to a series of deficiencies in how the 1972 statements were taken, including the fact the soldiers were ordered to make them, they were not conducted under caution, there was no access to legal representation and the Army policy of not asking soldiers to provide an explanation or rationale for their actions.

There were plainly deficiencies in the approach adopted by the (Historical Enquiries Team)

The focus of the legal wrangle over admissibility centres on statements and interviews the soldiers gave to the HET 38 years later. In their engagements with the HET in 2010 both soldiers accepted that they made the 1972 statements.

Lawyers for the soldiers expressed concern that the prosecution was trying to “launder” the inadmissible 1972 statements and get the evidence contained in them before the trial using the “backdoor” of the 2010 statements and interviews.

They also highlighted flaws in the HET process. They said the soldiers’ lawyers were not told that the 1972 statements were inadmissible and the veterans were under the impression they were participating in a fact-finding exercise to benefit the McCann family, rather than a criminal probe.

Mr Justice O’Hara questioned why when the veterans were cautioned prior to their HET interviews they were not informed what offence they were suspected of committing, namely murder.

Prosecution barrister Louis Mably conceded the soldiers should have been told.

“There were plainly deficiencies in the approach adopted by the HET,” he said.

Mr Mably insisted there was no set legal rule that evidence obtained as a consequence of the 1972 inadmissible statements was itself inadmissible as a consequence. He said it depended on the circumstances of the case.

He said Soldier A “voluntarily” relied on the 1972 statement in his 2010 engagement with the HET and he said Soldier C went further, offering new “incriminating” evidence of his involvement in the shooting during interview.

The Crown lawyer acknowledged that the various statements from the soldiers were the only evidence available to court capable of proving that they fired shots at Mr McCann on the day.

In response, the judge asked: “So without the interviews the case must inevitably fail?”

Mr Mably replied: “On that basis my lord, yes.”

Justice O’Hara said he would make his ruling on the admissibility issue at 11am on Friday.