The discovery suggests the Russian opposition leader was poisoned there.

Traces of the Novichok nerve agent allegedly used to poison Russian opposition leader Alexey Navalny were found in a water bottle in his hotel room in the Siberian city of Tomsk, where he was staying before he fell critically ill, Navalny’s colleagues said on Thursday.

The discovery suggests that Navalny was poisoned before he left the hotel and not at the airport, where they initially suspected he might have ingested the poison through a cup of tea.

Navalny fell critically ill on a flight from Tomsk to Moscow almost a month ago and was later airlifted to Berlin in an induced coma. Germany toxicology tests showed Navalny had been poisoned with a nerve agent from the Novichok family, a type of military chemical weapon developed covertly by Russia and used in the 2018 poisoning of the former Russian double agent Sergey Skripal in Britain.

Navalny’s team in an Instagram post on Thursday said a German lab had found traces of the nerve agent on one of several hotel water bottles that his colleagues in Tomsk went to collect immediately after learning he had fallen sick. Fearing Navalny had likely been poisoned, they decided to quickly gather anything that could have contained signs of it.

The Instagram post included a video showing Navalny’s colleagues in the hotel room wearing rubber gloves and collecting water bottles from the brand, “Holy Source.”

“There wasn’t any hope to find something special,” the Navalny team post read. “But since we were absolutely convinced that Navalny wasn’t ‘slightly sick’ or ‘overheated’ … it was decided to take everything that might hypothetically be of use and hand it over to German doctors.”

They wrote that the German lab found traces of the Novichok nerve agent two weeks later and that three other labs that took samples from Navalny confirmed it was the same he was poisoned with.

Navalny’s colleagues initially suspected he could have been poisoned at a cafe in Tomsk’s airport where he had drunk a cup of tea, the only thing they believe he’d ingested that morning.

“Now we understand that it was done before he left his room, to go to the airport,” Navalny’s colleagues wrote.

Navalny regained consciousness from the induced coma last week and appears to be recovering. This week he posted his first public message since the poisoning, along with a photo of himself sitting up and awake in his hospital bed surrounded by his family. His spokeswoman has said he intends to return to Russia once he recovers.

A number of opposition figures and Kremlin critics have been poisoned previously in Russia, who have struggled afterward to identify the poison because they have been unable to get samples fast enough to independent labs abroad and Russian authorities refused to investigate. Navalny’s team have accused the Kremlin of being behind Navalny’s poisoning and of deliberately pressuring Russian doctors who initially treated him to cover it up.

Navalny was taken to a hospital in Omsk, where the plane made an emergency landing after he collapsed on board. He was treated there initially before his family had him flown to Germany. Navalny’s relatives and colleagues accused authorities in Omsk of deliberately delaying Navalny’s evacuation to try to make it harder for German doctors to identify what he was poisoned with.

“It was pretty obvious the case will not be investigated in Russia. And that was right: nearly one month after, Russia hasn’t recognized Alexey’s poisoning,” Navalny’s team wrote.

Russia has denied any involvement in Navalny’s illness and has questioned whether he was poisoned, accusing Germany of making unfounded allegations. Chief doctors in Omsk have continued to insist tests on Navalny have found no signs of poisoning and they diagnosed him instead with an episode of low blood pressure.

Russian police have so far said they see no grounds for opening a criminal investigation into Navalny’s case since Russian doctors have not confirmed he was poisoned.

The head of Russia’s foreign intelligence service, Sergey Naryshkin, on Monday, said all Novichok stocks in Russia had been destroyed and insisted there was no evidence Navalny had been poisoned.

Two labs in Sweden and France have also confirmed Navalny was poisoned with a Novichok nerve agent. France’s President Emmanuel Macron called President Vladimir Putin this week, demanding Russia urgently shed light on the circumstances around Navalny’s poisoning.