A Sinn Fein assemblyman and a freelance sports commentator are believed to be among four people still held by police investigating an IRA bombing in 1972.
Nine people were killed in the no-warning bomb
Nine people, including three children, were killed when three car bombs exploded in Claudy, County Londonderry.
Sinn Fein's Francie Brolly and sports journalist Seamus Mullan are understood to be detained by police at Antrim.
A 58-year-old woman was one of those arrested by police re-examining the no-warning bombing in the village.
Police said two men aged 67 and 60 were detained in Dungiven, and a man, 50, was detained in the Portglenone area. The woman was arrested in Dungannon.
They were held by detectives on Tuesday morning, said a PSNI spokesman.
'Raise the issue'
Mr Brolly is an assembly member for the East Londonderry constituency.
Seamus Mullan is a freelance journalist who reports on Gaelic games for a number of media outlets, including BBC Northern Ireland.
Mr Brolly is an assembly member for East Londonderry
Sinn Fein's chief negotiator, Martin McGuinness, condemned the arrest of Mr Brolly.
He said the party would be raising the issue with the British and Irish governments and called for his immediate release.
The party's Mitchel McLaughlin also called the arrest of Mr Brolly "political policing".
Assistant Chief Constable Sam Kinkaid said new lines of enquiry had emerged as a result of reviewing the case.
"As a police service we are mindful of, and always uphold and protect the human rights of any individual we arrest," he said.
"Every person has a right to be deemed innocent until proven guilty and the police service is careful not to publicly disclose the names of those suspected of involvement.
"Equally we are mindful of the responsibility we have to investigate these events and to uphold the rights of those whose lives were taken from them in Claudy in 1972, the rights of loved ones who were bereaved and those whose lives were changed forever as a result of injury and loss."
In December 2002, the police said a priest, who had died, was involved in the Claudy bombing.
It also emerged that both the Catholic Church's cardinal at the time, William Conway, and the then Secretary of State, William Whitelaw, met to discuss the matter.