After the German invasion of Poland in September 1939, he volunteered as a chaplain to one of the Polish units and remained with them until their defeat.
Contrary to the prohibitions of the Nazi authorities that all liturgical rites be celebrated in German, he often used Polish during services and funerals.
He looked after the poor and met young people he knew from his previous work in organizations, especially in scouts.
Denounced by one of the residents of the district, whose confessions he had heard in Polish, in the summer of 1942 he was arrested by the Gestapo and imprisoned in Bydgoszcz prison.
In 1991, Świadek was included in a group of 108 Polish martyrs during World War II being considered for beatification.
At that time, an attempt was also made to rename the neighboring street (Kapliczna) in his honour but this was not accepted by the public authorities.