The head of the investigation, Christian Bonten, said he had narrowed the likely cause down to three possible theories but admitted the true trigger of the disaster may never be known.

“It’s frustrating,” he told reporters as he presented his 66-page appraisal.

The 14-metre (46-foot) high, cylindrical AquaDom aquarium — the largest of its kind — exploded in the early morning on December 16th last year, sending one million litres of water and all the fish inside spilling out into the hotel complex housing it.

READ ALSO: ‘Tsunami’: Hundreds of fish die as giant aquarium bursts open in Berlin hotel complex

Two people suffered light injuries from glass splinters and were treated in hospital, while dozens of the fish were recovered and taken to local zoos.

Bonten said his team had essentially ruled out sabotage early on and focused on possible material faults, either deriving from the construction two decades before or in the course of a major renovation in 2020.

After examining hundreds of shards of the acrylic glass that comprised the aquarium, he said he suspected defects in the adhesive used to join up the panels, damage incurred in replacing the base that led to small cracks, or a degrading of parts of the tank.

Bonten said he concluded the “tsunami”, as officials described it at the time, could not have been prevented by aquarium staff. “It happened suddenly and without warning,” he said.

Fabian Hellbusch, spokesman for Union Investment, which owns the complex, said the company expected all of the shops and restaurants inside to reopen by November and the hotel, whose rooms were not damaged, at a later point.

He said the lobby would be redesigned. “But it will not include an aquarium.”