He crossed the state border by accident
Not merely agents and political émigrés would cross the Iron Curtain. Former border guard Dalibor Plšek recalls that in 1968, the border guards arrested an elderly German gentleman. The elderly man saw a fire in Spálenec on the Czech side of the border and was afraid that the forest might catch fire. Thus he went to check personally if the forest wasn’t on fire but in doing so he accidentally crossed the border. The patrol detained him after the incident got cleared up he was officially returned to Germany.