Engineer Oliver Farrell tracked the use of the phone from early morning until the afternoon. He explained to the court how phones are normally routed through the nearest available masts, which make up the telecommunications network.

The results of his tracking of the calls are illustrated on the right of this page. He was asked whether his analysis of the location of the phone from around 8am until soon after 10am corresponded with Mr O'Reilly's account that he had travelled from his place of work in Bluebell industrial estate to Phibsborough/Broadstone bus garage. "It does not correspond, " Farrell said.

The series of calls suggested a journey northbound, culminating in two communications through Murphy's Quarry, which is half a mile from the O'Reilly home in The Naul, north county Dublin.

The calls then suggest a journey back south to the north inner city.

A later batch of calls from 10.38am until 11.05am were analysed. Farrell was asked whether these corresponded to O'Reilly's account of being at Phibsborough at that time.

"They are consistent with that description, " he said.

Under cross examination from defence counsel Patrick Gageby, Farrell admitted that the actual reach of the various transmitters could be greater than the theoretical reach.

An engineer employed with O2, Kareem Benabdullah was asked whether it was possible for a person to make a call in Phibsborough/Broadstone and have it routed through the Murphy's Quarry mast.

"Impossible, " he replied.