One of the most senior police officers involved with the Madeleine McCann case has said the searching of a reservoir in Portugal could be the “best chance” authorities have had in over a decade to find out what happened to the three-year-old girl.

German and Portuguese police investigating the suspect, Christian Brueckner, have begun scouring the desolate site 45 minutes from Praia da Luz in Portugal, where Maddie vanished in 2007.

Pictures have shown police tents being erected and officers scouring the shoreline at Arade Dam near Silves.

The spot is about 30 miles from the Ocean Club apartment where the three-year-old disappeared from while on holiday with her parents Kate and Gerry.

Jim Gamble was a top UK child protection officer and led a major review of the McCann case.

Talking to The Sun, he said he suspected German police had strong evidence against the prime suspect.

“They must have something definitive.

“Having worked with German police it grabbed my attention when the prosecutor was so sure in his assessment Madeleine was dead.

“They are obviously keeping what they have close to their chest and they don’t want to lose the evidential edge,” said Mr Gamble, who is now CEO of INEQE Safeguarding Group.

“I think we are looking at the best chance we’ve had in 16 years to find out what happened to Madeleine.”

It remains unclear why police are now searching the reservoir, but there are suggestions police have located video of the sex offender at the lake. In addition, low water levels could make any search easier.

Sources have said Christian Brueckner used to call the dam his “little paradise”.

“German authorities, prosecutors and investigators are normally very conservative – so when they do say something definitive you know they have the additional information,” said Mr Gamble.

“They have been absolutely adamant on two things, one, they have the right suspect, and two, that Madeleine is dead.”

Images from the remote lake have shown police investigators with spades and pickaxes poring over an area next to the water where Christian Brueckner was thought to spend time.

German police have insisted that Christian Brueckner is the man they believe took McCann – but three years after announcing him as a suspect, they have yet to bring charges.

In 2008, a year after McCann disappeared, a search of the dam turned up an 30 foot length of cord, strips of tape, and small bones – but none of this has ever been linked definitively to the case.