His Washington-based company received about £300,000 of cash donated by the public after Madeleine vanished from an Algarve resort in May 2007 at the age of three.
A private detective accused of exploiting the hunt for Madeleine McCann to fund his lavish lifestyle has been found dead.
Surrey Police said the death was currently being treated as “unexplained”.
He said: “Although his death is certainly not foul play, as has been suggested, there are certainly a lot of people who wished him ill. But he was also unique.
In an interview for a 2014 Channel 5 documentary, Halligen denied claims he misused money raised to find Madeleine.
“His house was full of empty drink bottles. A lot of people wished him ill but his death is almost certainly related to alcoholism.”
He was then extradited to the US in 2012 to face charges over an unrelated £1.3 million con, to which he pleaded guilty in 2013.