The raid took the Japanese authorities in Singapore completely by surprise. Never suspecting such an attack could be mounted from Australia, they assumed it had been carried out by local saboteurs, most likely pro-Communist Chinese guerillas. In their efforts to uncover the perpetrators, a wave of arrests, torture and executions began. Local Chinese and Malays, as well as interned POWs and European civilians were targeted in this programme. The incident became known as the Double Tenth, for 10 October, the day that Japanese secret police began the mass arrests.