A pensioner arrested in connection with the murder and disappearance of Jean McConville is a former IRA leader.
Ivor Bell, widely reported to have been a commander within the organisation in Belfast during the 1970s, was arrested in a raid on his home in Andersonstown yesterday.
Last night, widowed mother-of-10 Mrs McConville's family said they were surprised by the arrest more than four decades on from the murder.
They said they were reluctant to allow themselves to become too hopeful of progress in the hunt to bring their mother's killers to justice.
The 77-year-old was taken to Antrim Serious Crime Suite where he remained throughout the day as detectives questioned him about the killing.
Mrs McConville's IRA killers tried to silence her 11-year-old son days after she vanished.
Michael McConville was abducted, beaten and threatened at gunpoint by young republicans intent on keeping her disappearance quiet.
He told the Belfast Telegraph last night that his family was shocked by news of the arrest but was treating the development with caution.
"To be honest we are taking little interest in it until we see which way it falls," he added. "People are arrested for things all the time and not charged so we will sit back and let police do their jobs."
Police contacted the McConville family shortly after the arrest and just prior to it being made public.
The arrest sent shockwaves throughout republican circles.
Bell was reportedly a leading figure within the IRA from 1970 until the mid-1980s.
Asked if he knew Bell, Mr McConville said was aware of who he was but did not know him personally.
Mrs McConville was among 17 people abducted, killed and secretly buried by republican paramilitaries during the Troubles.
Members of the IRA claimed some of the victims had "informed" on their activities to the authorities.
Mrs McConville (37) was killed after she went to the aid of a wounded British soldier outside her home in west Belfast's Divis flats in 1972. The IRA claimed she was an informer.
Her remains were finally found at Shelling Hill beach in Co Louth in the Republic in August 2003.
It is understood Bell was at home with his wife when police arrested him at the west Belfast property.
A family member said he is currently in poor health and requires regular medication. They strongly denied he had anything to do with the disappearance of Mrs McConville.