They made a formal statement yesterday asking gardai to investigate the new line.
They met Garda Superintendent Fergus Healy and informed him that an underworld source had approached them, alleging that Wilson had killed Amy.
It is expected that their request will be passed on to Interpol and the Spanish police, as Wilson is currently serving a 23-year jail sentence in the Mediterranean country.
"We are hopeful there will be movement on this," Mr Mahon said.
"We believe the information we have is credible."
Dubliner Amy was just 15 years-old when she went missing near her home in Calahonda on the Costa del Sol, Spain, on New Year's Day 2008.
She had been living with her mother, brother Dean, and Mr Mahon in the Spanish town.
At the time of her disappearance, Wilson was living near the area where she vanished.
He had rented a farm in Coin, less than 30km away from Amy's home of Calahonda.
The source who approached Amy Fitzpatrick's family told them he had boasted about murdering her.
Audrey and Dave now want the area where Wilson was staying to be searched.
Wilson (29), from Ballyfermot, Dublin, has been linked to a string of unsolved gangland contract killings in Ireland thought to include those of Paul Reay in 2006 and Roy Coddington in 2007.
'Lucky' Wilson was sentenced last year to a 23-year jail sentence for the brutal killing of a British expat.
In June 2010, he shot expat Briton Dan Smith eight times from close range after racing home on his motorbike to fetch a gun following a drunken row over a girl.
It has now emerged that the girl was one of Amy Fitzpatrick's friends, and that the missing Dublin teenager had been spotted near the area where the shooting took place on the night she disappeared two years earlier.
Amy was spotted in the Costa del Sol town with an older man at the time and her family now believe him to be Wilson.
Audrey Fitzpatrick is to release a book this summer with further revelations about her daughter's disappearance, in the hope that it will help her campaign to find out the truth about the teen's disappearance.