Goncalo Amaral claims that Madeleine died in 2007 and Kate and Gerry McCann covered it up.
The unfounded claims sparked a huge police response both from the UK and abroad, and in 2008 Amaral published his first book – which resulted Kate and Gerry tried to sue him for libel.
And last week Portuguese supreme court judges in Lisbon ruled that he could publish his controversial first book on the case, called The Truth Of The Lie.
And now, the Express claims the former police chief is putting the finishing touches to his second book whilst on a break in Switzerland.
Mr Amaral worked on the 2007 case when Madeleine, then three, went missing from the apartment the McCanns were staying at in Praia da Luz as Kate and Gerry ate dinner with friends.
He was moved off the case and resigned six months later but wrote his book using police files as he put forward a theory she had died in the apartment.
The McCanns took legal action, saying there was no evidence and his work was defamatory.
The appeal hearing in Lisbon which ruled against the McCanns was held in private.
A spokesperson from their lawyer's office said: "This is a big disappointment and very bitter for us and for Mr and Mrs McCann."
Maddie’s parents could now lodge an appeal to the highest court in Europe, the European Court of Human Rights.
But a source close to the exasperated couple said: "I think the fight is finally over. They want to concentrate on finding Madeleine and don't think they have the time or energy to lodge yet another appeal," reports the Mail Online.
Meanwhile, reports have emerged that Kate is locked in a huge bidding war as major news outlets battle to try and sign her up for talks on the 10th anniversary of Maddie’s death.
One has told the McCanns: “Name your price!” reports The Sun.
"They have been bombarded with offers from media around the world.
"They’re already got 30 sitting on the table and are getting new bids every other day particularly from the big American networks,’" says a friend.
Maddie, if alive, would turn 14 in mid May just nine days after the anniversary.
This article originally appeared on New Idea.