A former Northern Ireland detective who has played a central role in the investigation into the disappearance of Madeleine McCann believes the latest searches will be very focused.
It comes as fresh searches got underway in Portugal into the disappearance of Madelaine McCann.
Police divers entered the water early on Tuesday at the Barragem do Arade reservoir, about 30 miles from Praia da Luz, where Madeleine went missing in 2007.
It has been reported that the prime suspect in Madeleine's disappearance, convicted sex offender Christian Brueckner, 45, spent time in the area between 2000 and 2017.
Brueckner, who has denied involvement in Madeleine's disappearance, was identified as a suspect by Portuguese officials in June 2020.
He is facing charges in Germany over a number of separate sex offences allegedly committed in Portugal during that time.
Jim Gamble said with better technology will help the searches and it will be interesting what unfolds.
“I think what's happening here is progressive…it’s the German police who have a very active and live investigation and they’ve got a prosecutor and a number of credible investigators who are all saying this is the person.
“They are revisiting the sites that he was known to frequently visit and let’s face it this is 35-45 minutes from the crime scene.”
Mr Gamble, who was a former head of the RUC special branch now works in online child safety. He led the initial UK investigation into the disappearance. He appealed to anyone who was in Praia da Luz 16 years ago particularly if they were out by the reservoir.
"The German authorities are positive," he added.
"I think they have information that quite rightly they aren't sharing with the wider public and that's why it will be interesting to see if the searches are focused or deliberate or whether it is going to be needle in a haystack.
"I think it will be very focused."
Portuguese police confirmed on Monday that they are co-ordinating searches in the Algarve at the request of German police and in the presence of British officers.
A brief statement from the prosecutor's office in the German city of Braunschweig confirmed the search but did not reveal why it was taking place.
Four teams of officers from the Portuguese Policia Judiciaria are involved in the operation, along with at least 20 of their German counterparts, Portuguese news channel SIC said.
Around a dozen officers with sniffer dogs were moving along the bank of the reservoir as part of the search.
Investigators believe he killed Madeleine, then aged three, after abducting her from a holiday apartment.
German authorities are expected to release a statement about the search later on Tuesday. It is not the first time the reservoir has been searched.
In 2008, Portuguese lawyer Marcos Aragao Correia paid for specialist divers to search it after he claimed to have been tipped off by criminal contacts that Madeleine's body was there.
The most recent search in Portugal in relation to her disappearance was in 2014, when British police were given permission to examine scrubland near where she vanished.
Earlier this month, Madeleine's parents Kate and Gerry McCann posted a short statement on their Find Madeleine Campaign website to mark the anniversary of her disappearance.
They said: "Today marks the 16th anniversary of Madeleine's abduction. "Still missing... still very much missed.
"It is hard to find the words to convey how we feel."
The police investigation continues, and we await a breakthrough."
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