In spite of the spiritual and pastoral nature of their mission, the secret service of the Soviet Union considered Catholic missionaries to the USSR educated in the Collegium Russicum to be spies of the Vatican, and treated them as such. Ján Kellner was arrested on December 9, 1940, after being handed to the authorities by a peasant he had approached for help. His initial interrogation lasted three days and three nights (December 17–19, 1940). He stated in detail that he had been preparing for a long time for his mission into the USSR, and that he planned to "cross the border in the region of Sambor, and then secretly make his way to Lwów. From there he would go to Moscow and get a job at some factory, and then he planned to attend meetings of militant atheists and speak out against atheism." He would do this with the intention of "preaching the teaching of Christ among young people, in order to foster the work of unifying the Churches." He was subsequently transferred to the special NKVD prison in Kiev, where he was subjected to a total of thirteen interrogation sessions. Following the attack of Nazi Germany on USSR on June 22, 1941 and triggered by an internal command from Moscow to review the lists of those arrested by the NKVD to identify those suitable for execution, he was sentenced to capital punishment as "an enemy of the people" on July 7, 1941 and shot dead the same day.