This is NOT the first time these boxes have been robbed. I can think of many reports of theft over the years I have been in Argentina. At one point the government was considering opening boxes to see if there was anything they could tax:
http://www.clarin.com/policiales/Robaron-seguridad-Banco-Provincia-Belgrano_0_401959972.html
http://www.clarin.com/policiales/Robaron-seguridad-Banco-Provincia-Belgrano_0_401959972.html