A sickening online chat between the prime suspect in the Madeleine McCann case and another paedophile ‘could be a hint’ as to who is responsible for her disappearance.

The three-year-old vanished from an apartment in the Algarve in May 2007 and convicted sexual predator Christian Brueckner has been identified as the key suspect because of his movements in Portugal at the time. 

German police have uncovered a vile exchange between Brueckner and another paedophile on his computer in which he writes explicitly about wanting to abduct and kill a little girl.

A public prosecutor leading the investigation, which has now dragged on for 16 years, says the conversation may provide a crucial clue because of the use of the letters ‘mm’.

In the chat, which was too sickening to be made public in full, Breuckner describes how he wants to ‘document’ his kidnap and murder of a child.

One message from Breuckner reads, ‘oh, if the evidence is destroyed,’ to which the other paedophile replies: ‘Mm.’

Hans Christian Wolters, a prosecutor in Braunschweig, told BBC’s Panorama: ‘Yeah, maybe it could be a hint. It could be. Of course, it’s important for us.’

When asked if it could be part of a ‘bundle of evidence that could convict Brueckner’, Mr Wolters said: ‘Yes, this could be something like that. That could be a piece for the big puzzle.’ 

Mr Wolters said he is ‘sure’ that the toddler is dead, that she was killed in Portugal and that they only have ‘one suspect’ – Brueckner. 

‘We think that he was involved in the disappearance of Madeleine McCann,’ he said.

‘And we think that he murdered Madeleine McCann. That’s our stand.’

The 46-year-old is currently behind bars in northern Germany serving a seven-year sentence for the rape of a 72-year-old American woman in Praia da Luz in 2005 – the same village where Madeleine went missing.

He is being held at a high-security prison locally named as the ‘Alcatraz of the North’ in Oldenburg, near Bremen, and is accused of a string of further crimes in the area between 2000 and 2017.

It’s alleged that he carried out two sex attacks on children and three rapes, two of which he reportedly filmed at his former residence in Praia da Luz.

The trial, which is expected to last at least one month, could begin as soon as February next year and is likely to be held at Braunschweig High Court after it was ruled that Brueckner can be tried in Germany for the alleged crimes.

German prosecutors have not yet charged Brueckner in connection with the disappearance of Madeleine and the case against him is not yet fully known. 

But his history as a convicted thief, child abuser and rapist is well documented and the recently discovered online chat evidence suggests that he appears to have fantasized about abducting and killing a young girl. 

Investigators also say his phone puts him near the ground floor apartment 5A on Rua Dr Agostinho da Silva where Madeleine was staying when she disappeared while on holiday with her parents Kate and Gerry McCann. 

After getting hold of his phone number from May 2007, transmitter data showed he received a call near apartment 5A between 7.32pm and 8.02pm on the night Madeleine vanished – she was reported missing at 10pm.

Mr Wolters says he is ‘sure’ that Brueckner was near the apartment that night but when questioned as to who was on the other end of the line, he admitted: ‘We don’t know. We know only the number.’

He said that the call is ‘very important’ to the investigation.

‘We have some kind of evidence,’ Mr Wolters said. ‘So maybe these are pictures, videos, chats, documents, something like that.’

In May this year, an extensive three-day search operation was carried out by police at a reservoir near Praia da Luz that Brueckner once called his ‘little piece of paradise’ and would stay at in his campervan.

Mr Wolters said: ‘At the reservoir, we are searching for evidence, not for the body of Madeleine.

‘I can’t speak about the results because the investigation of the things we found there is still ongoing.’

Officers had previously found child pornography on USB sticks buried under Brueckner’s dead dog at an abandoned factory in eastern Germany he owned and used to live at.

It’s thought that USB sticks may be among the items investigators were searching for at the reservoir in Portugal, the BBC reported.

When asked about when the case could be solved, Mr Wolters added: ‘I hope that we will come to an end in the next year. 

‘Maybe we need some more time but I hope that we will finish the investigation in the next year.’

It also emerged that Portuguese police travelled to London earlier this year to apologise to Madeleine’s father Gerry in person for the way he and his family were treated.

Brueckner has denied killing Madeleine and wrote a string of dark letters from his prison cell to protest his innocence.

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