Convicted double killer Colin Howell is set to be questioned about a new allegation of serious sexual assault.
Police have made arrangements to have the 58-year-old former dentist brought from jail on Wednesday for interview, informed sources disclosed.
The allegation relates to an historical incident, according to one of those familiar with the case.
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 Londonderry 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 from 1998 and 2008.
Now he faces questioning about a further sexual assault allegation.
Howell is to be produced from Maghaberry Prison and taken to the Laganside Courts complex in Belfast.
He is then expected to be transferred to nearby Musgrave Street police station where the interviews are due to be held.