Two former paratroopers deny murdering Joe McCann almost 50 years ago, a court has heard.
Official IRA member Joe McCann (24) died after being shot in the Markets area of Belfast in 1972.
The veterans, referred to in court proceedings as Soldiers A and C, entered not guilty pleas at the start of their trial at Belfast Crown Court today.
They will remain anonymous throughout the proceedings.
Opening the case, a prosecution lawyer told the court that Mr McCann was a senior member of the Official IRA who was suspected of involvement in a number of attacks carried out by the republican group.
He said the shooting took place after an RUC Special Branch Officer attempted to arrest him on Joy Street in the Markets area of Belfast. Mr McCann evaded detention and ran away.
The Crown lawyer said at that point soldiers A and C, and another now deceased paratrooper - solider B - opened fire. They had been manning a checkpoint in the area at the time.
The lawyer said shooting Mr McCann in the back as he ran away was unlawful and not justified.
"On any view of the facts, the level of force used was unreasonable," he said.
In legal exchanges over disclosure issues prior to the Crown's opening statement, a lawyer representing one of the soldiers insisted the force used was reasonable.
She said Mr McCann was suspected of involvement in murders and could have committed more if he had evaded arrest.
The lawyer said soldiers faced a "binary choice" of either firing to effect the arrest or Mr McCann getting away.
The two men wore suits and face masks and were seated at the side of the courtroom, in an area usually reserved for the jury.
The trial is expected to last four weeks.
It is one of a number of legacy cases, referring to incidents which took place before the signing of the Belfast Agreement in 1998, on which the Public Prosecution Service has taken decisions.
Former veterans minister Johnny Mercer is also attending Belfast Crown Court to watch the proceedings.
The ex-British Army officer left his ministerial role last week after expressing frustration at a lack of progress on legislation to protect British veterans who served during the Troubles from prosecution.
The Conservative MP was accompanied in court by Veterans Commissioner Danny Kinahan.
Mr Mercer said the trial of the two former soldiers is “unfair”.
“I think in any conflict, it is messy, it is unpleasant, it is a horrible process to go through for both sides,” he added.
“What I don’t think is – 50 years later – you get a truly accurate picture of what happened.
“I think it is unfair to try and apply today’s standards of operations and retrospectively apply them to that time and try to get justice.
“I have huge sympathy on all sides but we need to move on in Northern Ireland.
“What is happening today, I don’t think is fair and that’s why I am here.
“The reality is today, as we stand here, there are two individuals in court for something that happened 50 years ago.
“They served their country, they did their best. War is messy and we need to find a solution for everybody.”
Mr Mercer denied he is “interfering” in the trial, adding he is there to “learn about the process”.
A small group of protesters, some dressed in military uniform, were picketing outside the court in Belfast ahead of the trial.
Demonstrators held banners expressing opposition to historical prosecution of former British soldiers.