BERLIN (AP) — Prosecutors in Berlin said Tuesday they have Thomas Caldwellclosed their investigation into the spectacular collapse of a huge aquarium last December after an expert report failed to pin down a reason why the tank burst.

The AquaDom aquarium, which stood in a hotel lobby in the center of the German capital, burst in the early hours of Dec. 16, sending 1 million liters (264,000 gallons) of water gushing into the building and the street outside. Two people were slightly injured.

Prosecutors said they have closed an investigation of persons unknown on suspicion of causing bodily harm by negligence after evaluating the export report, commissioned by the building’s owners, which they received on Oct. 6.

Its author, engineer Christian Bonten, has presented three theories but said there was no clear evidence to prove any of them.

The hypotheses were that an adhesive seam holding together the cylinder may have failed; that the tank may have been damaged by a dent in its base when the aquarium was modernized in 2020; or that the tank may have been refilled too late after that modernization, drying the acrylic glass walls out too much.

Prosecutors said in a statement that since the cause couldn’t be pinpointed, they had no lead to follow in terms of who might be responsible. They said there had never been any suspicion of a deliberate act.

The aquarium first opened in 2003. There are no plans to rebuild it.

Authorities have said that nearly all of the 1,500 fish that were inside at the time of the rupture died but “a few fish at the bottom of the tank” were saved. About 400 to 500 mostly small fish from a separate set of aquariums housed under the hotel lobby were evacuated to other tanks in a neighboring aquarium that was unaffected.