Sinn Féin leader Gerry Adams is still being questioned by Northern Ireland police in connection with the 1972 murder of Jean McConville.
Mr Adams, 65, spent a second night in custody after presenting himself at Antrim police station on Wednesday evening.
He has denied involvement in the death of the mother of 10.
Secretary of State Theresa Villiers has said she was told on Monday that Mr Adams was expected to be questioned.
She said she was told by one of her officials, who had been told by a member of the PSNI.
"I noted it and obviously started to think through the potential consequences," she said.
"There has been, and there will be, no political interference in prosecutions in this case.
"I don't think we can expect the police, in their decisions, to take account of the electoral calendar."
Ms Villiers said the government was "in touch with Washington keeping them informed of the situation here".
Meanwhile, Mrs McConville's daughter, Helen McKendry, has said she is "ready to name names".
In an interview with the BBC's Newsnight programme she said: "I do not fear the IRA anymore. I will happily give the names that I know to the police."
Asked if she feared for her life by divulging such information, she said: "No, what are they going to do to me? They've done so much to me already in the past 42 years, what are they going to do? Come and put a bullet in my head? Well, they know where I live."
On Friday, it emerged that it was Prime Minister David Cameron who had phoned Sinn Féin's Martin McGuinness the previous evening to discuss Mr Adams' arrest.
Mr Cameron also spoke with First Minister Peter Robinson.
It is understood Mr Cameron reiterated his view that there was no political interference and it was a matter for the police.
Sinn Féin has claimed the arrest was deliberately timed ahead of elections in three weeks' time. The Democratic Unionist Party (DUP) said it showed no-one was above the law.
Mr McGuinness, Northern Ireland's deputy first minister, said during Thursday's conversation he had pressed Mr Cameron on killings related to the state.
"The Police Service of Northern Ireland is duty bound to fully and energetically pursue every investigation and I support and encourage them to do so," he said.
"But I know that some investigations are pursued more vigorously than others."
First Minister Peter Robinson said the arrest "strengthens our political process in Northern Ireland for people to know that no-one is above the law".
"I would suggest to you that it would be political policing if the PSNI had not questioned those that were deemed to have been involved in any way," the DUP leader said.
Former Northern Ireland Secretary Peter Hain described Mr Adams' arrest as a "serious moment for Northern Ireland's politics.
"Regardless of the particulars of this case, about which I cannot comment except to say that when we were seeking the truth about the Disappeared in the period 2006 to 2007, Gerry Adams was co-operating with me and with the Police Service of Northern Ireland to try and establish the truth about these cases," he told Radio Ulster's The Nolan Show.
"I know for a fact, because he told me this that he felt very strongly that these individual cases of the Disappeared were wrong and that he totally identified with the families concerned.
"He seemed to me to be genuinely concerned in seeking to get to the bottom of what happened and genuinely mortified about the plight of the families."
Kidnapped in front of children
Mrs McConville, a 37-year-old widow and mother of 10, was abducted and shot by the IRA.
Her body was recovered from a beach in County Louth in 2003.
Mrs McConville, one of Northern Ireland's Disappeared, was kidnapped in front of her children after being wrongly accused of being an informer.
The claim that she was an informer was dismissed after an official investigation by the Northern Ireland Police Ombudsman.
The widow was held at one or more houses before being shot and buried in secret.
The Disappeared are those who were abducted, murdered and secretly buried by republicans during the Troubles.
The IRA admitted in 1999 that it murdered and buried at secret locations nine of the Disappeared.
The Independent Commission for the Location of Victims' Remains was established in 1999 by a treaty between the British and Irish governments.
It lists 16 people as "disappeared". Despite extensive searches, the remains of seven of them have not been found.
Jean McConville's remains were found in 2003 by a man walking at Shelling Hill beach, near Carlingford.
Last month, Ivor Bell, 77, a leader in the Provisional IRA in the 1970s, was charged with aiding and abetting the murder.
There have also been a number of other arrests over the murder recently.