Madeleine McCann disappearance suspect Christian Brueckner has spoken for the first time since being made an "official suspect" in the case by Portuguese prosecutors, almost 15 years after the young British girl vanished while on holiday in Portugal. 

The 42-year-old child sex offender was interviewed by German detectives at Oldenburg jail in northern Germany on Thursday, where he is currently serving a seven-year rape sentence after being convicted of raping a 72-year-old woman in 2005 in Praia da Luz. 

He is also being probed over the 2004 rape of Irish tour rep Hazel Behan, who has waived her anonymity, and a sex assault on a 10-year-old girl at Praia da Luz just a month before Madeleine vanished. 

In a five-page letter seen exclusively by the Daily Mail, Brueckner stressed he was not there at the time and was now "the most known bad person in the world and did nothing - well almost nothing". 

The letter was sent from his prison cell to a woman whom the Daily Mail is not identifying. 

"I wasn't kidnapping anybody and of course, I wasn't killing anybody," he wrote. 

A waiter tapes a picture of missing 3-year-old girl Madeleine McCann on a restaurant's window in Praia da Luz, southern Portugal, in May, 2007. Photo / AP 

"I'll go further, I'll tell you I wasn't attacking anybody after I was 18. 

"I made some silly mistakes when I was younger but who hasn't?" 

The Daily Mail said he then referred to the McCann case. Brueckner said: "Perhaps I was a suspect after all they found out about me. 

"Drug dealer, breaking into houses, living in cars and there was something with kids when I was 17. 

"But they had not even one proof (sic) that I was involved with the McCann case. And they still don't have it. 

"I know why. Because they have no hairs or anything from Maddie what means (sic) that nobody can put anything like that into my stuff to find it. 

"The idea behind that all perhaps was to make the BKA (German police) and German prosecutor famous as well known all over the world as the smartest organisation ever." 

The Daily Mail say that Brueckner noted there was "no proof" against him and that German authorities were leaking information to portray him in a poor light. 

"I know of about five open cases against me, all of them including raping and abusing. 

"They have manipulated the truth in such an unprofessional way that I am laughing. 

"I still have not lost my sense of humour. Even in this critical situation. This is what keeps me alive." 

Kate and Jerry McCann in 2020, holding an image of what Madeleine would have looked like at 16. Photo / Supplied 

Madeleine went missing from her family's holiday apartment on May 3, 2007, a few days before her fourth birthday. 

Shortly afterwards, her parents Kate and Gerry, who live in Rothkey, Leicestershire, were made suspects and questioned at length several times before they were cleared. 

Madeleine's disappearance has been the source of documentaries, podcasts and a Netflix series, with police identifying hundreds of people as potentially significant to the case. 

The disappearance of Madeleine, or "Maddie" as she is known in Britain, sparked a massive search effort and an international media frenzy. 

No trace of her has ever been found. 

Last year her parents, Kate and Gerry, marked what would have been their daughter's 18th birthday. 

"We hang on to the hope, however small, that we will see Madeleine again," they said last May. 

"As we have said repeatedly, we need to know what has happened to our lovely daughter, no matter what. We are very grateful to the police for their continued efforts. 

"We still receive so many positive words and good wishes despite the years that have gone by. It all helps and for that, we are truly grateful – thank you."