 Soon afterwards, Jan Kiliński, one of the leaders of the uprising, presented documents found in the archives of the Russian embassy about Kossakowski's being on the Russian payroll.Most of the citizens of Warsaw, whose support was crucial to the uprising, demanded that Kossakowski and others found to be acting on Russia's behalf against the Commonwealth should be executed.Their stance influenced the revolutionary Criminal Court, and Kossakowski, together with Józef Ankwicz (leader of the Permanent Council) and hetmen Piotr Ożarowski and Józef Zabiełło were convicted of treason and sentenced to hanging on 9 May.