The way the IRA dealt with the bodies of those they abducted and murdered was "wrong", Sinn Fein leader Gerry Adams has said.
Gerry Adams said the way the bodies were dealt with was wrong
New levels of cooperation between the IRA, Sinn Fein and the Irish government should see the recovery of the remaining five Disappeared, he said.
Mr Adams also revealed that IRA members involved in the killings have visited burial sites with a forensics expert.
The Sinn Fein president was speaking at a briefing for journalists on Tuesday.
"There were not primary sources involved in all cases because in some cases these people themselves had either died or been killed in the intervening years," he said.
"By primary sources I presume that it is people who were there when the killings took place - either transporting those who were killed, or in fact killed those who were killed or buried those who were killed."
BBC Northern Ireland's home affairs correspondent Vincent Kearney said Mr Adams revealed that the IRA has met a forensics expert seven times during a 10 month period.
He said they had also visited the sites where the IRA believes the five remaining bodies are buried.
"On some occasions, IRA members present included people who carried out the killings, people the Sinn Fein leader called primary sources," he said.
"A forensic expert is said to have submitted a report to the Irish government in February, making a number of recommendations that he believes could lead to the bodies being found.
"Gerry Adams called on the government to act on that report, and acknowledged that what the IRA did was wrong."
Jean McConville was abducted and murdered in 1972
Nine people murdered and secretly buried by the IRA during the 1970s became known as the Disappeared.
The remains of four have been found, the latest in 2003.
This was mother of 10 Jean McConville, who the IRA claimed at the weekend had been an "informer" who passed information to the British security forces.
On Friday Northern Ireland's Police Ombudsman Nuala O'Loan said she had found no evidence that Mrs McConville had passed information to the security forces.
However, the IRA later insisted a "thorough investigation" confirmed that the mother of 10 "was working as an informer for the British army".
In 1999, the IRA admitted they had killed Mrs McConville and several other of the Disappeared, but alleged some of them had been informers.
Mrs McConville, who was a widow, was killed after she went to the aid of a fatally wounded British soldier outside her home in west Belfast's Divis flats.
Her remains were finally found at Shelling Hill beach in County Louth in the Irish Republic in August 2003.
Mr Kearney said that at Tuesday's briefing Mr Adams "would not be drawn on the issue of Jean McConville".
"The fact that Gerry Adams has gone public with details of this secretive process at this time clearly demonstrates that the fate of the disappeared is once again firmly on the political agenda, as DUP leader Ian Paisley has called for the recovery of the bodies," he said.
"Republicans clearly know that to move forward, they have to be seen to be attempting to deal with the past."
In a statement the Irish government said it was involved in discussions with the Northern Ireland Office about how to respond to the forensic report.
It said the families of the Disappeared will be informed of the outcome of these discussions "shortly".