Convicted double killer Colin Howell has been questioned about a new allegation of serious sexual assault.
The 59-year-old former dentist was brought from jail to be interviewed at a Belfast police station yesterday in connection with a complaint relating to an historical incident, an informed source disclosed.
He was later returned to custody pending a report to the Public Prosecution Service.
Howell is currently serving a minimum of 21 years in jail for the murders of his wife and former lover Hazel Stewart's police officer husband.
The bodies of Lesley Howell (31) and Constable Trevor Buchanan (32) were found in a fume-filled garage in Castlerock, Co Derry in May 1991.
Police originally believed they had died in a suicide pact after discovering their partners were having an affair.
Nearly two decades passed before Howell suddenly confessed to both killings.
He pleaded guilty to the murders in 2010, implicated Stewart in the plot and went on to give evidence against her at her trial.
In March 2011, she was unanimously convicted of both murders and ordered to serve at least 18 years behind bars.
Since then the former Sunday School teacher has failed in a series of attempts to have the verdicts overturned.
Howell is also serving a five-and-a-half-year sentence for sexually assaulting five female patients while they were under sedation at his dental surgery in Ballymoney, Co Antrim.
He committed those offences over a 10-year period between 1998 and 2008.
Police originally planned to have him prosecuted back in January for questioning about the new sexual assault allegation.
But, following a last-minute postponement, those interviews did not take place until yesterday.
Howell was brought from Maghaberry Prison to the cells at Laganside Courts, and then transferred directly to the nearby Musgrave Street police station.
He was questioned for a number of hours before being taken back to jail.
A PSNI spokesman said yesterday: "A 59-year-old male was interviewed by police today and a file will now be prepared for the Public Prosecution Service."
Earlier this month, it was revealed that creditors of Howell are to be repaid at least some of what they are owed after he went bankrupt seven years ago.
As well as the families of Ms Howell and Mr Buchanan, his estate could face claims from victims who were sexually assaulted at his dental practice.