Three men and a woman, including a Sinn Féin MLA, have been arrested by detectives investigating the IRA bombing in Claudy, Co Derry, in 1972.
Six adults and three children were killed when IRA car bombs went off in the village without warning on July 31st, 1972.
Today, a 67-year-old man and a 60-year-old man were arrested in Dungiven, Co Derry, while a 50-year-old man was held in Portglenone, Co Antrim, and a 58-year-old woman was detained in Dungannon, Co Tyrone.
Sinn Féin chief negotiator Martin McGuinness said: "This is the latest and among the most blatant examples of political policing seen here in recent times.
"As has become the norm with this type of political policing, selected media outlets were briefed about the identities of those arrested."
Republicans were expected to hold a protest against the arrest outside Dungiven PSNI barracks later today.
Police began a fresh investigation into the bombing under a senior detective in 2002 when they revealed a local Catholic priest had been part of the IRA gang which bombed the village.
Fr James Chesney, who died in 1980, was named as the priest concerned. Police alleged a cover-up had been hatched between the British government and the-then Catholic primate Cardinal Conway to keep the priest's involvement secret when rumours began that he was linked to the bombing.
Democratic Unionist Assembly member Ian Paisley Jr insisted anyone found guilty of the Claudy bombing should not be included in any amnesty for outstanding historic terrorist crimes.
The North Antrim MLA said: "The innocent victims caught up this indiscriminate and atrocious massacre have waited over three decades to see the murder of their loved ones resolved.
"The DUP has long said that the 1,800 unsolved murders in Northern Ireland must be resolved to the satisfaction of the innocent victims.
"I hope that today's actions by the police leads to convictions, however, the government must now remove from any person who could be convicted of this heinous crime an amnesty that would not see them serve a single day in jail for their part in mass murder."
Additional reporting PA
