Maurits Sonépouse and his brother Salomon tried to flee to Switzerland in August 1942 through occupied France, crossing somewhere near Montbéliard. They were arrested on Swiss soil and put into jail in Porrentruy on August 21. On the next day, they were turned back to France. They managed however to escape all dangers on their return to Amsterdam, where Maurits was arrested one month later, while Salomon remained free and survived.
Source: Register of the jail in Porrentruy, cited in SPIRA, Henry, «La frontière jurassienne au quotidien», Geneva, 2010, p. 481 and p. 286.