The lead investigator with an expert team searching for the so-called Disappeared has said that he is "hopeful for a successful outcome" from the latest search in Co Monaghan for the remains of Columba McVeigh.
The teenager, from Donaghmore in Co Tyrone, was 19 when he was abducted, murdered and secretly buried by the IRA in 1975.
The Independent Commission for the Location of Victims' Remains (ICLVR) searching for the so-called Disappeared victims of the Troubles has already carried out several searches at Bragan Bog, in north Co Monaghan.
However, each of the six operations, which took place since 1999 and covered more than 26 acres of bogland, were unsuccessful.
After the most recent search ended without a breakthrough in November 2023, a review was carried out into the parts of the bog that had not already been searched.
It was through this analysis that what is described as a relatively "small piece of ground" was identified as not having been searched.
A team of personnel attached to the ICLVR is conducting a search of the area with the use of machinery, including a number of diggers.
The search was planned to commence in the spring of this year. However, it could not proceed due to environmental issues.
The ICLVR has said it worked closely with the National Parks and Wildlife Service to resolve these issues and the operation was launched on Monday 18 August.
It is expected to take at least five weeks to complete.
Lead investigator with the ICLVR, Eamonn Henry, said the McVeigh family has been informed and are fully supportive of this latest search.
He added that: "The ICLVR believes we are searching in the right area based on the criteria provided. We are hopeful for a successful outcome as we search on behalf of the McVeigh family to find Columba."
The commission was set up by the British and Irish governments during the peace process to investigate the whereabouts of 17 people murdered and secretly buried by republican paramilitaries during the Troubles.
While 13 of the so-called Disappeared have been formally found, Mr McVeigh, former monk Joe Lynskey, British Army Captain Robert Nairac and Seamus Maguire, who was in his mid-20s and from near Lurgan in Co Armagh, remain missing.
Mr McVeigh's brother, Oliver, said that the family is cautiously optimistic about this latest search.
"We are optimistically hopeful. As long as they are searching in the bog and it's an organised search, there's a better opportunity of finding him," he told RTÉ's News at One.
"We are happy at that but we're going to be extremely happy whenever we find him, if we find him. We have a huge dollop of optimism, you know what I mean, and caution thrown in here.
"But this is the seventh time we have been here before, and I suppose each time we have had our hopes built up as well, and they have been sort of taken away from us again, but maybe this time will be the time."
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Oliver McVeigh also spoke about the lasting impact that his brother's disappearance has had on his family.
"My mother went to her grave. We had only learned a few years before what had happened [to Columba] and she died.
"She thought it was all going to happen very quickly, and that she would get him and burying him in the grave with my father, who died just a year previously, and then she said she would be hoping to go in with them whenever she dies.
"But she's dead now 17 years and it still hasn't happened. So that is the thing, that is the sad that I have. I mean, I just only have to think of my mother and what she went through down the years.
"She was on the bog and she was in the bog with people and workers. So, it doesn't even bear thinking about what she was thinking at the time her son was buried there. Is it any wonder she died of a stroke," he added.
Additional Reporting Kate Egan & PA
