Updated 10.30am.

Christian Brueckner, the German prime suspect in the 2007 disappearance of British toddler Madeleine McCann, was on Tuesday cleared of all charges in a separate sex crimes trial.

Brueckner, 47, could "not be convicted of the acts he is accused of", said presiding judge Uta Engemann, clearing him of five counts of rape and child sex abuse.   

The case has been closely watched because the  47-year-old  could be set free as early as next year. He is currently behind bars, serving a sentence for raping a 72-year-old US tourist in 2005 in Praia da Luz -- the same Portuguese seaside resort where Madeleine went missing two years later.

Prosecutors in his latest trial have called for him to be jailed for a further 15 years, describing him as a "dangerous psychopathic sadist".

Brueckner was revealed as a suspect in 2020 in a bombshell development in the "Maddie" investigation, one of the highest-profile missing persons cases in history.

On May 3, 2007, a few days before her fourth birthday, "Maddie" disappeared from her family's holiday apartment in the Algarve village in Portugal as her parents dined with friends at a nearby restaurant, sparking one of the biggest searches of its kind in recent years.

German prosecutors have not charged Brueckner over Madeleine's disappearance, although they have said they are certain that Madeleine is dead.

But two years ago, Brueckner was charged with five separate counts of rape and child sex abuse allegedly committed in Portugal between 2000 and 2017.

He had been on trial for those charges in the western German city of Brunswick since February.  

Doubts about evidence

Prosecutors accused Brueckner of entering the holiday apartment of a woman aged between 70 and 80, tying her up and beating and sexually assaulting her.

In another case, he was accused of entering a young Irish woman's apartment via her balcony while she was sleeping, threatening her with a knife and raping her several times.

He was also accused of exposing himself in front of a 10-year-old German girl on a beach and to an 11-year-old Portuguese girl at a playground.

The charges came about as a result of investigations into the "Maddie" case, according to prosecutors.

However, the defence raised serious doubts about the quality of the evidence.

In the first rape allegation, one of the key witnesses was Helge Busching, a former acquaintance of Brueckner who claimed to have seen video footage of the incident.

But the footage was no longer available and the defence labelled Busching, who also has a long criminal history, an unreliable witness.

The Irish woman testified at the trial but there was no concrete evidence other than her account of the incident.

Notebooks seized from Brueckner detailing his sexual fantasies were also used as evidence. But, despite their disturbing content, they provided no direct link to the alleged crimes.

Missing without trace

Brueckner's lawyers in July won a bid for an arrest warrant against him to be cancelled as there was no longer deemed to be an "urgent suspicion" that he committed the five offences.

The move was a technicality as Brueckner remained behind bars, but his lawyer Friedrich Fuelscher argued that the court's decision was a "clear sign that the defendant will be acquitted". 

Brueckner's current rape sentence runs until September 2025, according to Christian Wolters, a spokesman for the prosecution in Brunswick, though Fuelscher has said the defendant could be free as soon as the spring.

Three-year-old Madeleine went missing from her family's holiday apartment in Praia da Luz in Portugal's Algarve region in May 2007 while her parents dined at a nearby tapas bar.

Despite a huge international manhunt and global media attention, no trace of her has been found.

Investigations are continuing in the "Maddie" case and will proceed regardless of the outcome of the ongoing trial, prosecutor Wolters told AFP.

"At present, I am unable to say when we will be able to conclude these investigations and with what result," he said.