One of them , Colonel Hans Oster , an `` Abwehr '' ( German military intelligence ) officer , began in March 1939 to pass along information to his friend , the Dutch military attaché in Berlin Major Gijsbertus J. Sas .
One of them was Colonel Hans Oster , a German intelligence officer . In March 1939 he began to pass information to his friend , a Dutch military officer in Berlin Major Gijsbertus J. Sas .