More than eight years after her disappearance, Amy Fitzpatrick is still being treated as a high-priority case by the Garda missing persons bureau.
The 15-year-old vanished without trace as she walked the short distance from a friend's house to her home at the Costa del Sol in Spain on the night of January 1, 2008.
Since then, she has been the subject of a long-running investigation by Spanish police and the gardai while Mahon and his wife, Audrey Fitzpatrick, spent thousands of euro to keep the case in the public spotlight.
Although few believe that Amy is still alive, she continues to be officially regarded as a missing person.
Mahon, who was yesterday convicted of the manslaughter of Amy's older brother, Dean, is not suspected of having any involvement in the teenager's disappearance.
A senior garda officer said last night: "At this stage, there is no evidence either here or in Spain to suggest that Amy is dead and we continue to co-operate with the Spanish police whenever a new line of inquiry emerges."
After Audrey and Dave returned to live in Dublin, two senior garda officers flew to Spain for face-to-face talks with local police after an earlier meeting with the couple in Garda HQ in the Phoenix Park.
As a result of that meeting, arrangements were made for separate briefings on developments in the case from the Spanish investigators with the couple and also with the family of Amy's father, Christopher.
Extensive inquiries in both countries were also carried out after Dave Mahon said they had been informed by criminal sources that notorious killer and alleged gangland "gun for hire" Eric 'Lucky' Wilson had boasted in a pub that he had killed Amy.
Mahon claimed that the information they had received was credible and that they were close to solving Amy's mystery disappearance.
He said he had information from six different criminal sources that Wilson murdered Amy and at the time of her disappearance he had lived in apartments in the Riviera del Sol area, close to the Hotel Oasis, which was frequented by Amy to use their internet connection.
However, investigations established that Wilson, from Cremona Road in Ballyfermot, was not in the Costa del Sol at the time Amy went missing and was ruled out by gardai and the Spanish police as a suspect.
A senior garda admitted last night: "We are back to square one but we continue to liaise with the Spanish authorities and any help they require from us will continue to be provided."