The unnamed man was detained a month ago in Saxony-Anhalt state, on a European arrest warrant, accused of "abetting a terrorist organisation linked to the terror attacks, including on the Bataclan concert hall, on November 13, 2015 in Paris," according to German police and judicial authorities.
The German authorities said that he had been targeted in a separate investigation against two Bosnian citizens on suspicion of violating military weapons control laws.
From Germany to Belgium
On 13 November, 2015, gunmen killed 130 people in a string of coordinated attacks in and around the French capital.
The Islamic State armed group, which was battling to create a caliphate in Syria and the region, claimed responsibility. The attacks were allegedly coordinated in Brussels.
Five months later, 32 people were killed in suicide bombings in the Belgian capital Brussels. Hundreds were injured. IS claimed those attacks too.
The same cell is believed to have been instrumental in both terror attacks.