Navalny previously poisoned by a nerve agent, as has happened to others who get on Putin’s bad side.
Navalny had successfully exposed the immense and spectacular corruption within the Kremlin mafioso machine. The Russian people supported him. That was too much for the chief of the Deep State in Moscow to handle. All Putins opposition leaders are now rotting in Gulags or are being killed.
Putin would lose any debate against any opposition leader. So better kill them all... Just like the old Soviet Union, Russia has now become the Neo Soviet Union.