Members of the police team investigating the Bloody Sunday massacre will travel to England this month to interview eight former soldiers about the 14 people who died.
While the eight will not be arrested, they will be questioned under caution as part of a High Court ruling made after they mounted a legal challenge.
The ex-soldiers had won their legal action preventing them from being taken to Northern Ireland for questioning.
Thirteen people were killed by the Parachute Regiment in the Bogside in Londonderry on January 30, 1972.
Another victim died in hospital four months later.
Seven former paratroopers took the High Court action after Soldier J, who lives in Northern Ireland, was arrested and taken to Antrim PSNI station for questioning about the deaths of William Nash, John Young and Michael McDaid, as well as the shooting of Alexander Nash.
The police team, led by Detective Chief Inspector Ian Harrison, informed the relatives of the victims of plans to carry out more interviews in April and warned these could run into May.
He also stated in his correspondence to the relatives that due to the High Court ruling he did not intend to "release any details which could potentially lead to the identification of the former soldiers".
Even though he said he understood the families might want this information, he did not want to risk further delays to the investigation.
Kate Nash, whose brother William was killed on Bloody Sunday, said the timescale set aside for the interviews concerned her.
She said: "I had asked who these soldiers were but in his letter to us, Ian Harrison said he would not release that to us so we have no idea who these eight are.
"We have no idea who the soldiers are that they plan to interview in April; we have no idea when exactly these interviews are being held.
"These interviews, while they are welcomed, are not going to begin until later in March and could continue into May when there is an election which could throw up all kinds of delays.
"My biggest fear is that there will be an attempt to offload this investigation to the Historical Investigation Unit, where it will be swallowed up and forgotten about.
"There has never been any real effort to properly investigate the deaths of our loved ones because it is now well over five years since the Saville Inquiry report was published and we are no further forward, really."
The investigation was under threat of closure in January 2015 when the Chief Constable said that due to cuts in his budget the probe would have to be abandoned.
However, after challenges it was reinstated with a time frame of four years and a total budget of £4m.