The almost two-decade-long mystery surrounding the disappearance of Madeleine McCann took another twist after the main suspect walked free from a German prison.

A German man suspected of being behind one of the 21st century's biggest missing persons mysteries walked free from a prison near Hanover on Wednesday after completing a lengthy sentence for rape. Briton Madeleine McCann has not been seen since she disappeared from the Portuguese holiday apartment where she was staying with her family on May 3, 2007. File Photo UPI UPI

Sept. 17 (UPI) -- The main suspect in the disappearance of Madeleine McCann, the British child missing since 2007, was freed Wednesday from a prison outside of Hanover in northwestern Germany after completing a sentence for an unrelated rape conviction.

Police confirmed that Christian Bruckner, 48, left Sehnde Prison, accompanied by his lawyer, after authorities, who had been desperately trying to find a way to keep him incarcerated, conceded there were no legal grounds for his continued detention.

It was unclear if he would be required to wear an electronic tracker on his ankle as demanded by prosecutors who believe he is responsible for three-year-old Madeleine's disappearance 18 years ago from a resort in southwestern Portugal, which they are treating as a homicide.

German prosecutors also want Bruckner, a convicted pedophile and drifter who spent much of the early 2000s traveling between different European countries, to have to report to authorities on a regular basis and surrender his passport, citing him as a flight risk as they pursue an 8-year-long investigation.

State prosecutors say they have circumstantial evidence connecting him to the crime, including that his mobile phone logged in the area where Madeleine vanished from a holiday apartment where she was staying with her family, as well as confessions Bruckner allegedly made to three separate witnesses.

However, the evidence so far has been insufficient for an indictment and Bruckner has never been charged with any offense related to Madeleine's disappearance.

Bruckner was convicted and sentenced to a seven-and-a-half-year prison sentence for raping an elderly American woman in 2005 in Praia de Luz, from where Madeleine disappeared 18 months later.

In October, he was found not guilty of rape and child sex abuse charges in a trial in Braunschweig, east of Hanover, after the court ruled there was insufficient evidence and that the prosecution's witnesses were "unreliable."

The acquittal had knock-on effects on the McCann investigation and prosecutors' effort to keep Bruckner in preventative custody beyond the end of his sentence because their case relies on some of the same witnesses.

Forensic searches directed by German police investigators, including the use of divers, were carried out at a remote reservoir Bruckner was known to frequent, 30 miles away from Praia de Luz, two years apart in May 2023 and this summer.

The search in June also focused on a 120-acre area between the Ocean Club resort where the McCann family were staying and a house Bruckner lived in at the time.

Bruckner this week declined to be interviewed by Scotland Yard detectives from Britain's Met Police, which has also been investigating the case for the past 18 years -- although as a missing persons case due to differences in the German and British legal systems.

The Met's Detective Chief Insp. Mark Cranwell confirmed Monday the force's request had been rejected, but that Bruckner remained a suspect.

"We have requested an interview with this German suspect but, for legal reasons, this can only be done via an International Letter of Request, which has been submitted. It was subsequently refused by the suspect. In the absence of an interview, we will nevertheless continue to pursue any viable lines of inquiry," said Cranwell.