The trial of Mr John Gilligan for the murder of journalist Veronica Guerin resumed yesterday after a one-month adjournment over Christmas.
The Special Criminal Court was told about a key "protected witness", Charles Bowden. The trial continues today.
The prosecution has claimed that Mr Gilligan was "in control and command" of a criminal gang that imported and distributed large amounts of cannabis and that he organised the murder of Ms Guerin.
Det Insp O'Mahony, of the National Bureau of Criminal Investigation, told the court that he met Charles Bowden at Kilmainham District Court in April 1997.
He said Bowden went with him to point out five locations - Killakee forest car-park, Pine forest car-park, a field adjoining a Jewish cemetery at Oldcourt Road in Tallaght, a premises at Greenhills industrial estate in Walkinstown and a premises at the Kylemore industrial estate in Ballyfermot.
It was the ninth day of the trial of Mr Gilligan (48), with addresses at Corduff Avenue, Blanchardstown, Dublin; Jessbrook Equestrian Centre, Mucklon, Enfield, Co Kildare; and HM Prison Belmarsh, London, who has pleaded not guilty to the murder of Sunday Independent crime reporter Veronica Guerin (37) at Naas Road, Clondalkin, Dublin, on June 26th, 1996.
Det Insp O'Mahony said that Bowden had admitted to gardai that he had imported four kilos of cocaine. He said a file had been forwarded to the DPP and any decision about prosecuting Bowden for the cocaine importation would have been taken by the DPP.
The detective inspector said that when Bowden returned to Ireland in March 1997, he told gardai he was willing to co-operate fully with them and to give evidence.
He said Bowden had told them that he had supplied cocaine to a man called "Arthur" in what the detective inspector agreed were "off the record" conversations.
Det Insp O'Mahony agreed that in a statement to gardai in October 1996, Bowden said he initially thought the drugs operation was controlled by Brian Meehan but from conversations he had with other people he then believed it was Mr Gilligan.
The detective inspector also agreed that in a statement in March 1997 Bowden had said that he believed another man, who cannot be named by order of the court, was deeply involved in the drugs business and was a partner of Mr Gilligan.
Bowden also admitted giving guns to this man which were "sweeteners for the politicals". Det Insp O'Mahony said he was not aware that this man had contacted gardai on the night of Ms Guerin's murder to protest his innocence.
He said he was aware that this man had been in hospital on the day of the murder after having had an accident while racing at Mondello.
Earlier yesterday, the defence had the evidence of protected witness Mr John Dunne adjourned because it was not ready to cross-examine. Mr Gilligan also denies 15 other counts alleging the importation of cannabis and firearms and ammunition offences.