Alexei Navalny’s team was at breakfast in the Siberian city of Tomsk when they received word that the opposition leader had fallen violently ill on his flight home to Moscow.

The activists raced to the room in the Xander hotel he’d left hours before and scrambled to collect evidence. "It was obvious to us that Navalny hadn’t just gotten a bit sick,” they recalled in an Instagram post Thursday. "We decided to take everything that might be of use.”

A plastic Svyatoi Istochnik (‘Holy Source’) water bottle they picked up would weeks later be found by a German military lab to have traces of Novichok, the weapons-grade nerve agent first developed by the Soviets. The use of a banned chemical weapon in the Aug. 20 attack has left German authorities with little doubt that the operation was ordered from the highest levels of the Russian government, according to three officials in Berlin familiar with the findings.