Updated: 12.10

Gardaí investigating the disappearance of Dublin schoolboy Philip Cairns are understood to have already conducted a walking search of a field on the Tallaght side of the Dublin mountains.

The Irish Independent reports the land was used by the convicted paedophile Eamon Cooke to transmit a signal for his pirate radio station.

The planned search follows reports that people saw Cooke using a digger on the property more than 30 years ago, and may have buried a container 20 feet underground on the site.

13-year-old Philip Cairns disappeared on his way back to school in Rathfarnham in Dublin in 1986.

However, security correspondent with the Sunday Times John Mooney warned that it must be remembered Philip's mother has said her son did not know Eamon Cooke.

He told Newstalk: "If Eamon Cooke was known to Philip Cairns and the two of them had been in communication, that is a massive problem for the guards, because that shows that the first investigation had not been carried out properly."

Gardaí yesterday renewed an appeal for information over the schoolboy's death.

Irish Independent crime journalist Paul Williams told Newstalk that witnesses saw the serial child abuser using a digger in the field more than 30 years ago.

At the time, he said, people believed Cooke was trying to construct an illegal transmitter system for his pirate radio station.