Northern Ireland First Minister Peter Robinson has said any police inquiry into Bloody Sunday must include the role of current Mid-Ulster MP Martin McGuinness.
He was speaking after police said they would launch a murder investigation into the deaths of 13 people shot by soldiers on Bloody Sunday in 1972.
Mr Robinson said the deputy first minister had already admitted he was prominent in the IRA at the time.
Police have yet to set a date for the investigation to start.
The move comes after the PSNI and Public Prosecution Service reviewed the findings of the Saville inquiry, which said none of those killed in the shootings in Londonderry were armed.
One of the inquiry’s other findings was that Mr McGuinness was present at the time of the violence and “probably armed with a sub-machine gun” but did not engage in “any activity that provided any of the soldiers with any justification for opening fire”.
Mr Robinson said: “How could you avoid an inquiry into that and say that we’re going to have an inquiry into the Army personnel that were there.
“The deputy first minister has openly admitted that he was in charge, if that was the case then there has to be an investigation if you’re investigating the Army.”
In response Mr McGuinness said he would have no problem co-operating with the police investigation, but rejected claims he was armed with a machine gun that day.
He said it was clear the PSNI had no interest in questioning him and were instead focused, on what he called, “the murderous activities of members of the parachute regiment”.
“I totally and absolutely reject that - it didn’t happen, it’s not true,” he said.
“I didn’t fire a machine-gun, I didn’t even have a machine-gun and that’s where it rests.”
Asked for his response to what Mr Robinson had said, he replied: “I don’t have a problem with that at all, no difficulty whatsoever.”
The investigation is expected to take at least four years and involve a team of 30 detectives.
PSNI Chief Constable Matt Baggott made the announcement of the investigation to the Northern Ireland Policing Board on Thursday.
“It is a matter that I think we should be investigating and will be investigating,” he said.
On Friday a spokesman for Prime Minister David Cameron said: “Whether or not a police force decide to reopen an investigation is entirely a matter for the police force.”
Together with other staffing and technical support the cost is likely to exceed £10m”
The chairman of the Police Federation for Northern Ireland, Terry Spence, said that where there was sufficient evidence of criminality by either police officers or Army personnel prosecutions should follow.
However, he said it would be more appropriate for the killings to be investigating by the Historical Enquiries Team, which is looking into murders carried out during the Troubles.
“Why are police resources, already under enormous pressure, to be devoted to a particular event when the unsolved murders of 211 RUC police officers are being investigated along with over 2,000 civilian unsolved murders through the Historic Enquiries Team?” he asked.
“The requirement of the criminal investigation into the Bloody Sunday deaths as presently envisaged, is scoped as 30 specialist officers over four years.
“Together with other staffing and technical support the cost is likely to exceed £10m.”
Bloody Sunday occurred on 30 January 1972 - a civil rights demonstration through the streets of Derry in the north-west of Northern Ireland ended with the shooting dead of 13 civilians by the British Army.
Fourteen others were wounded.
The Saville Inquiry cost £195m and was the longest-running and most expensive inquiry in British history.
Lord Saville was appointed in 1998 by then Prime Minister Tony Blair to look into the events of Bloody Sunday.
It followed an earlier official inquiry in 1972, led by the Lord Chief Justice Lord Widgery, which was described as a “whitewash” by the families of the victims and their supporters.