Portuguese police are reportedly seeking DNA samples and fingerprints from British holidaymakers who stayed at the resort where Madeleine McCann went missing five months ago.
The move is said to have come after detectives uncovered evidence of a possible kidnapper.
Reports this morning say the samples have been requested because experts have been unable to identify a number of traces found in the Ocean Club resort in Praia da Luz.
Some of the traces are from the apartment where the McCanns were staying.
The apartment was reportedly searched for five hours again yesterday by police investigating the case.
Superintendent Stuart Prior, who is heading the British investigation into the four-year-old's disappearance in Portugal is said to have written a letter to holidaymakers asking for their help, according to a newspaper.
He is said to have told tourists in the letter: "I have now been asked by the Portuguese investigation team to arrange for DNA samples and fingerprints to be taken from holiday-makers living in the UK who were staying at the Ocean Club Resort."
Saying the collection was a "routine" practice he adds that obtaining of the samples, “will help the Portuguese police to eliminate samples they have taken and not yet been able to identify”.
Leicestershire Constabulary, which is co-ordinating the investigation in Britain on behalf of the Portuguese authorities, would not confirm whether such letter had been sent.
The young girl went missing from the family holiday apartment in Praia da Luz, southern Portugal on May 3. Both of her parents Kate and Gerry McCann have been named as suspects in the case by Portuguese authorities though charges have yet to to be laid.
The McCanns have continually denied involvement and called for Portuguese police to concentrate on finding Madeleine.