Published Monday, 23 April 2012
Search teams are concentrating on an area near Emyvale in Co Monaghan (© Pacemaker)
The 17-year-old from Donaghmore, Co Tyrone, was abducted and murdered by the IRA in October 1975.
He had been working in Dublin at the time of his disappearance.
The Independent Commission For The Location Of Victims' Remains (ICLVR) is investigating land close to an area of bogland where previous searches have taken place.
Last week, hundreds of mature trees on the bog were cut down to open the site up for excavation and allow forensic archaeologists to inspect roots.
The missing man's brother, Oliver McVeigh, said he is convinced the teenager's remains lie in the vast bog.
He said his family is sure Columba's body was dumped on the remote upland in north County Monaghan, which has been overgrown by huge forestry over the last 30 years.
The family is convinced his body is there. We are 100% certain but it's just a question of locating the spot in this bog.
"It's still a big strain on the family and it was his mother Vera's wish to find her son that has kept us going.
"I can still see the anguish on her face. It will never leave me."
Jon Hill, senior investigator with the commission, said they remained "hopeful" that Columba would be found.
However, he said the search is located at a "bleak, difficult area" of land.
"We have to remain cautiously optimistic - [that] would be the term you would use.
"Of course we are hopeful or we wouldn't be here in the first place."
He said that there was "a realistic possibility" of finding him.
"There's also a realistic possibility that we wouldn't."
To date, the remains of nine Disappeared have been found. Seven still have to be located.
In February, it emerged that fresh information obtained from the IRA would result in this new dig.
The development came one day after the commission issued a further plea to the public for new information. The dig is expected to last four weeks.
© UTV News