Berlin — Christian Brueckner, the convicted sex offender named by German authorities as the prime suspect in the disappearance of British toddler Madeleine McCann almost two decades ago, has refused to be interviewed by U.K. police just days before his expected release from prison. 

The 49-year-old German national is due to walk free by Wednesday after serving a seven-year sentence for a separate crime, the rape of a 72-year-old American woman in the same region of Portugal from which McCann vanished during a vacation with her family. 

While Brueckner remains under formal investigation over McCann’s 2007 disappearance, he has never been charged in connection with the case and he continues to deny any involvement.

His decision to decline the London Metropolitan Police’s formal request for an interview is being seen as a setback in the long running search for answers in the case that has frustrated investigators in Britain, Portugal and Germany for years.

British Investigators hoped to question Brueckner to clarify key details about his movements in Praia da Luz, the resort town in Portugal’s southern Algarve region from which McCann, then three, disappeared. She vanished from her family’s rental apartment while her parents had dinner nearby. 

For many connected to the case, Brueckner‘s looming release represents both a pivotal moment and an obstacle. Authorities have been weighing how much oversight they can reasonably maintain over the convicted sex offender once he is no longer behind bars.

Prosecutors in the city of Braunschweig have petitioned the regional court in Hildesheim for what’s known as supervisory oversight, a form of monitoring similar to parole that could allow them to impose strict conditions on Brueckner after his release, possibly including an ankle tracking tag. 

Brueckner could also be required to declare a fixed place of residence, inform authorities of any change in address or workplace, and face restrictions on where he is permitted to travel. Such restrictions could include barring him from areas linked to his past crimes. He could also be prohibited from leaving Germany without requesting explicit approval from authorities. 

Brueckner’s attorney Friedrich Fuelscher declined to comment when asked by CBS News about the possibility of his client being subjected to supervisory oversight measures.

A regional court will ultimately decide what measures, if any, to implement following Brueckner’s release. 

Even if supervisory oversight measures are granted, they are unlikely to satisfy critics who believe the circumstantial evidence linking Brueckner to the McCann case should dictate more close cooperation with British investigators. 

His refusal to answer U.K. detectives’ questions means they won’t get a chance to push him about inconsistencies in his alibis or to confront him directly with witness statements they have gathered over the last 18 years.

The McCann case remains one of the world’s most high-profile missing persons investigations.

Brueckner has been at the center of the inquiry since German prosecutors publicly identified him as a suspect in 2020, citing phone records and his history of violent crimes in Portugal’s Algarve region. But no charges have ever been brought against him in the McCann case, as the circumstantial evidence has been deemed insufficient to move forward with charges under German law.