 In January 1948, the United Nations brokered a fragile cease-fire, but almost immediately both sides violated the truce in multiple incidents and the Dutch forces made preparations for a new operation against the rebel forces.It was at this time, while being on leave at Sukabumi, that Princen took on September 25, 1948, the irrevocable step which shaped the rest of his life.He crossed the Line of Demarcation into rebel-held territory, and via Semarang reached Yogyakarta, the provisional capital of the self-proclaimed Indonesian Republic – where the suspicious Indonesian nationalists promptly threw him into their own prison.