On 1 September 1950, in the middle of a holiday in Italy, Pontecorvo abruptly flew from Rome to Stockholm with his wife and three sons without informing friends or relatives. On 2 September he was helped by Soviet agents to enter the Soviet Union from Finland. His abrupt disappearance caused much concern to many of the western intelligence services, especially those of Britain, Canada and the United States, that were worried about the escape of atomic secrets to the Soviet Union, and of Finland and Sweden, through which Pontecorvo and Marianne had been allowed to travel without valid passports and visas.