Investigators are beginning a fresh search for Joe Lynskey, who was abducted and murdered by the IRA in 1972.
Preparatory work will start today to clear a small area of trees in Oristown, Co Meath, with the dig beginning within days.
The former Cistercian monk, who later joined the IRA, was kidnapped in west Belfast in August 1972.
He became known as one of the so-called Disappeared - 16 people abducted and secretly buried by republicans in the 1970s and 1980s.
The search is being led by the Independent Commission for the Location of Victims' Remains (ICLVR).
Lead investigator Geoff Knupfer said: "We carried out an extensive search for Joe Lynskey in nearby Coghalstown in 2015.
"During that search we found the remains of Seamus Wright and Kevin McKee, but unfortunately we drew a blank in relation to Joe Lynskey.
"As we do after every unsuccessful search we go back and review all the information that we have pulled together to see if there are other lines of inquiry to be pursued.
"That's what we've done in this case and as a result we are going to look at quite a small area of woodland at Oristown near where we found Brendan Megraw in 2014."
He said they would start work as soon as the land is cleared of trees and contractors and forensic archaeologists can begin.
"We anticipate that this will not be a long search either way.
"The Lynskey family have been informed and they know only too well that there is no guarantee of success but we will continue to do everything we can."
Of the 16 Disappeared, the remains of 13 have been recovered.
The remaining three are Mr Lynskey, Columba McVeigh who was kidnapped in 1975 and British soldier Captain Robert Nairac, taken in south Armagh and killed by the IRA in 1977.
Mr Knupfer appealed for information on the three cases, saying: "Any information provided to the ICLVR is held in complete confidence and can only be used for the location of the Disappeared and cannot be shared with other agencies for any other purpose.
"Anyone with information on any of the outstanding cases should contact the ICLVR on 00800 555 85500, by writing to ICLVR, PO Box 10827, Dublin 2, or via the website www.iclvr.ie."