Police are currently describing the death as "unexplained".
56-year-old Kevin Halligen was found dead by police in his girlfriend's home after they were informed that he had been "feeling unwell".
Halligen, who was born in Dublin and had dual Irish and American citizenship, had been hired by Madeline McCann's parents and the Find Madeline Fund on a £500,000 (a little over €560,000) contract in 2008, a year after the three-year-old had gone missing.
The McCann's hired Halligen when they became frustrated that the Portuguese police had failed to find any clue as to their daughter's case, but subsequently ended their contract with him in 2009, as
Sky News reports that they believed he failed to deliver on the work they had paid him for.
Following this, Halligen had been extradited to America where he pled guilt to fraud charges over a previous contract, and was jailed but was freed due to time served in custody, and was returned to the UK.
Police in Surrey, where Halligen was found, released a short statement:
"We were called to an address in Cobbett Hill Road, Normandy, Guildford, on Monday following a report of a man in his 50s having been taken unwell, who subsequently died. The death is being treated as unexplained and a file will be passed to the coroner's office in due course."
