Aged 30, in 1941, Prassek met Karl Friedrich Stellbrink, a pastor at the nearby Lutheran Church. They shared disapproval of the Nazi regime, and Prassek introduced Stellbrink to his Catholic colleagues, Hermann Lange and Eduard Mueller. The four priests spoke publicly against the Nazis – initially discreetly – distributing pamphlets to friends and congregants. They copied and distributed the anti-Nazi sermons of Bishop Clemens August von Galen of Münster. Then, following the 28 March 1942 RAF air raid, after which Stellbrink tended wounded, he delivered a Palm Sunday sermon which attributed the bombing to divine punishment. Stellbrink was arrested, followed by the three Catholic priests. Prassek had been denounced by a Gestapo informer. Arrested in May 1942, he was sentenced to death by the People's Court in June 1943, in the "Lübeck Christians’ Trial", and executed on 10 November 1943 in Hamburg, alongside the other priests. Resigned to martyrdom, Prassek wrote to his family: "Who can oppress one who dies". The mingling of the blood of the four guillotined martyrs has become a symbol of German Ecumenism.