What are the Boston tapes?
A key part of the investigation into the abduction and murder of Jean McConville are tapes that were held in a US college.
The 'Belfast Project' was launched in 2001 and was designed to become an oral history of the Troubles.
Former loyalist and republican paramilitaries gave a series of candid interviews that chronicled their involvement in the Troubles.
It was directed by the writer and journalist Ed Moloney, with the interviews carried out by two researchers.
Recordings of these interviews were held in a library at Boston College and became known as the Boston tapes.
Loyalists were recorded by Wilson McArthur, republicans by the former IRA prisoner Dr Anthony McIntyre, who has since become a writer and academic.
The deal was that the former paramilitaries would tell their stories in secret, on the understanding that the recordings and transcripts would only be made public after their deaths.
The testimonies of David Ervine of the Progressive Unionist Party, and the former IRA commander Brendan Hughes, who have both since died, formed the backbone of a book by Ed Moloney, and a television documentary.
In those, Hughes made some frank admissions.
He said that he had organised Bloody Friday, the day on which the IRA detonated more than 19 car bombs in Belfast in the space of an hour.
Nine people were killed, 130 were injured. Images of police officers shovelling the mutilated bodies of the victims into bags are some of the most enduring of the Troubles.
Hughes also spoke of his once close friend, the Sinn Féin leader Gerry Adams.
Hughes named him as overall commander of the IRA's Belfast brigade.
He also claimed that Mr Adams had controlled his own squad within the IRA, known by the organisation as "the unknowns".
This, according to Hughes, was the group responsible for the 'Disappeared', those who were kidnapped, murdered and secretly buried by the IRA.
Mr Adams has strenuously denied the claims, and has pointed out that he and Brendan Hughes came to differ on the route Sinn Féin was taking.
In the latter years of his life, Hughes had become an ardent critic of his former friend.
However, another former IRA member later gave an interview to a newspaper journalist, in which she admitted that she had also taken part in the 'Belfast Project'.
Dolours Price, who died in 2013, had been one of the IRA gang that bombed the Old Bailey in 1973.
In that interview, she allegedly claimed to have been the person who drove Mrs McConville to the place where she was murdered by the IRA in 1972.
In 2011, the Police Service of Northern Ireland (PSNI) began a legal bid to gain access to the interviews held by the college.
Following a lengthy court battle, the PSNI was given transcripts of interviews by Brendan Hughes and Dolours Price.
Mr Moloney has said that Ms Price did not make claims about the Disappeared in the Boston College interviews.
However, it has since emerged that another interview was conducted with Dolours Price after the Belfast Project was completed and is now in the hands of the PSNI.
For his part, Mr Adams said he had nothing to fear from any disclosure, and denied all of the accusations levelled at him.
He was arrested by the PSNI in May 2014 and the transcripts formed part of the material that was put to him over four days of questioning about his alleged role in the killing of Jean McConville.
Mr Adams, who has always denied he had anything to do with the murder, said the Boston project's interviews with three former IRA members had "formed the mainstay for my arrest".
Shortly after his arrest, Boston College said it would return interviews to former paramilitaries who contributed.
Last year, a subpoena was issued following a request from the Police Service of Northern Ireland, ordering Boston College to hand over all tapes relating to Anthony McIntyre, a former IRA member who was a researcher on the project.
He had recorded a number of interviews detailing his own IRA activities, as well as interviewing others.
Lawyers acting for him moved to prevent the interviews being handed over to the PSNI. They argued in Northern Ireland's High Court that the move was "just a fishing expedition".
Last September, Anthony McIntyre was granted leave to seek a judicial review of the police's decision to issue a letter requesting the confidential recordings.