A SICK online exchange between prime suspect in the Madeleine McCann case Christian B and another paedophile has been revealed.
The vile messages "could be a hint" that finally leads investigators to answers for the toddler's grieving family, according to the case's lead prosecutor.
Convicted sexual predator Christian B is yet to be formally charged but was named by cops as the prime suspect after the three-year-old vanished in 2007 while on a family holiday in Praia da Luz, Portugal.
Sixteen years on, German prosecutor Hans Christian Wolters has told BBC's Panorama that online messages sent between Christian B and and another paedophile might include a reference to Madeleine.
In the chat discovered on one of Christian B's computers, the suspect detailed his desires to abduct and kill a little girl - and "document it".
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He then spoke of "destroying evidence" to which the paedophile replied: "mm."
Of the exchange, Mr Wolters said: "It could be a hint.
"Of course, it's important to us. It could be piece for the big puzzle."
While "MM" are Madeleine McCann's initials, it's unclear exactly what the suspect was referring to in the message.
The suspect's extensive online chat history is known to contain disturbing messages pointing to his paedophile fantasies.
He allegedly discussed kidnapping and sexually abusing a child in a chatroom exchange in September 2013, and claimed he would make a lot of films if he were to capture a "little one".
Christian B is currently serving a seven-year sentence for the brutal rape of a pensioner in Portugal at a high-security prison known as the "Alcatraz of the North" in the German city of Oldenburg.
He could face trial as early as February next year for a string of heinous alleged crimes including three rapes and two sex attacks on children, it was reported this month.
Two of the alleged rapes are said to have taken place at his former residence outside Praia da Luz, where Madeleine disappeared.
German authorities have indicated a trial related to Madeleine's case could take place shortly after Christian B's upcoming trial, The Olive Press reports.
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Mr Wolters added: "I can only say that we have only one suspect at the moment.
"[She died] in Portugal and we think maybe we know where it happened."
In the Panorama documentary, a woman said Christian B ran a "rebellious gang" in Würzburg, Germany when he was a teenager.
She said: "They were very rebellious and destroyed a lot of stuff.
"They were always out and about, escaping through windows and gone."
Others who encountered Christian B in the years following Madeleine's disappearance spoke of his violent and aggressive nature.
A bar manager, Brigitte Szegedi, recalled the "fits of rage" she witnessed him have with other patrons, while a former employee of the suspect claimed he once confronted him with a knife.
The unnamed man told the BBC: "He had this long knife and wanted to stab me. He was drunk or on drugs.
"His eyes glistened like mad and he was filled with rage."
The man added Christian B's girlfriend, who was a teenager when the suspect was in his late 30s, was assaulted by him.
He claimed: "I met her at the bus stop and asked her where she had got those strangulation marks from and she told me he strangled her and beat her.
"She was scared stiff of him, she told me a lot of things. She was really scared of him."
The main said he had no doubts Christian B was capable of the crimes he is accused of, explaining: "In the beginning he is sweet but once you get to know him, he is a psychopath.
"He has several faces. This man is highly, highly dangerous."
A third man, who previously employed Christian B in the Algarve in Portugal, said Christian B once broke his nose in an argument.
It was also revealed in the programme that Portuguese police apologised to Madeleine's parents for the way they handled their daughter's disappearance.
Kate and Gerry McCann were made arguidos - or suspects - in the investigation into Madeleine’s disappearance.
Both were questioned by Portuguese detectives, who believed they had staged an abduction and concealed their daughter’s body.
Kate McCann has said she was offered a deal to admit covering up her daughter’s death in exchange for a shorter sentence.
The couple’s arguido status was lifted in 2008, but they remained under suspicion in Portugal for years.