The nerve agent allegedly used to poison Russian opposition leader Alexei Navalny was detected on an empty water bottle from his hotel room in the Siberian city of Tomsk, suggesting that he was poisoned there and not at the airport as first thought, his team said on Thursday.

Navalny fell ill on a flight in Russia last month and was airlifted to Berlin for treatment. Laboratories in Germany, France and Sweden have said he was poisoned by Novichok nerve agent, a poison developed by the Soviet military. Russia denies this and says it has seen no such evidence.

A video posted on Navalny’s Instagram account showed members of his team searching the room he had just left in the Xander Hotel in Tomsk on August 20, an hour after they learned he had fallen sick in suspicious circumstances.

“It was decided to gather up everything that could even hypothetically be useful and hand it to the doctors in Germany,” the post said.

The video of the hotel room shows two water bottles on a desk, and another on a bedside table. Navalny’s team members are seen placing items into plastic bags.

“Two weeks later, a German lab found traces of Novichok on the bottle of water from the Tomsk hotel room,” the post said.

Previously, Navalny’s aides had said they suspected he had been poisoned with a cup of tea he drank at Tomsk airport.