The first of the group of about a dozen people known as "the disappeared", who were abducted and killed by the IRA, was kidnapped in 1972.
The issue has been repeatedly raised with the republican leadership and the Sinn Fein president, Mr Gerry Adams, has met some of the affected Belfast families, promising to do what he can to have the victims located.
The party has been pressurised by the churches, the Government, and internationally, to exert its influence on the IRA to seek the recovery of the missing people taken away in a period from 1972 to 1980. The US President, Mr Bill Clinton, was among those urging that action be taken and senior republicans have privately acknowledged that the issue must eventually be settled.
The Families of the Disappeared have a list of people whose remains they want identified and returned. According to a list provided by the lobby group founded in 1995, the first of the abductions involved two teenage boys, Kevin McKee and Seamus Wright, kidnapped in Belfast in 1972.
In December 1972, Mrs Jean McConville, who lived in Divis Flats, Belfast, was taken from her home and never seen again.
In 1974 John McElroy and Seamus Wright from Andersons town, west Belfast, went missing on their way to work. Mr Wright was not related to the man of the same name who disappeared two years previously in the city.
Also in 1974, Brendan Megraw was taken from his home in Twinbrook, Belfast, but considerable mystery still surrounds the abduction and it is not clear if the IRA was involved.
In 1977, Colm McVeigh (17), from Dungannon, disappeared.
The same year, the undercover British soldier, Capt Robert Nairac, was captured by the IRA in south Armagh. He was shot but his body was never found.
In 1978, John McClory (18) and Brian McKinney (22) were taken and never seen again.