German detectives believe the prime suspect in the Madeleine McCann case may have written letters about her as Portuguese Police examine whether her body was dumped in a well.
Detectives probing into the life of Christian Brueckner are hunting for the supposed letters and have asked ex-girlfriends for notes the convicted sex offender may have sent them in the past.
The move comes after it was revealed Portuguese police had been looking at the possibility McCann's body was dumped in wells near Brueckner's old home, according to claims.
Weekly Portuguese newspaper SOL said police had already undertaken some work aimed at establishing whether the missing youngster's body might be in one of them on the basis that she is dead as the German authorities insist.
"In the spirit of cooperation with their German counterparts, the PJ have been undertaking tasks which include work on wells near a house Christian Brueckner lived in in the south of Portugal.
"The aim is to ascertain whether there exists any possibility the British girl's body could have been left there."
It went on to claim: "As far as the Portuguese investigators are concerned, everything the German authorities have got so far continues to be insufficient to be able to exclude other lines of inquiry or other suspects.
"Within the PJ it's felt that the evidence that exists at the moment is insufficient to be able to bring a formal accusation."
The wells investigated are believed to be near Brueckner's old rented ramshackle cottage just over 3km from where Maddie went missing.
The property has a well right beside it as well as others dotted around the countryside nearby.
Neighbours said earlier this week they were only aware of searches in the wider area six years ago led by Met Police which turned up nothing new.
Last week German prosecutor Hans Christian Wolters admitted they did not have enough evidence yet to charge Brueckner but believe they are close should someone come forward with a vital piece of information.
"We expect that she is dead, but we don't have enough evidence that we can get a warrant for our suspect in Germany for the murder of Madeleine McCann.
"At the moment, we also don't have enough proof for a trial at court, but we have some evidence that the suspect has done the deed.
"That's why we need more information from people, especially places he has lived, so we can target these places especially and search there for Madeleine."