On that day, the 1956 Suez War had just begun. Though Jordan was not involved in the war, a 5 p.m. to dawn curfew was declared on all the Arab villages in the area close to the Jordanian border. However, many of the Arabs of Kfar Kassem were away from the village when the curfew was declared and were not informed about it. As they returned to the village after 5 p.m., they were lined up and shot dead by Israeli Border Police.
According to the Border Police battalion commander Shmuel Melniki, he was given the order to kill the villagers by brigade commander Issachar Shadmi, but Shadmi denied it. Melniki claimed that "the order was not of a kind that did not conform to the spirit of the times".
The initial reaction of the Israeli government was to impose strict censorship on the incident, while conducting an internal enquiry. However, some private individuals and one communist member of the Knesset managed to publicise the event despite the censorship. The resulting court-martial sentenced eleven Border Police to lengthy prison terms, but all of them were out of prison by November 1959 due to presidential pardons or remissions.
Soon after his release, Melniki was promoted and put in charge of security for the Dimona nuclear reactor. Shadmi was found guilty of a minor administrative offence and fined a token amount (a small coin). Financial compensation was paid to the families of the victims.
As a result of the Kfar Kassem case, the Israeli Supreme Court made a landmark ruling on the obligation of soldiers to disobey manifestly illegal orders. Judge Halevy stated that "The distinguishing mark of a manifestly illegal order is that above such an order should fly, like a black flag, a warning saying: 'Prohibited!'."