If this commander's quote represents the rules of engagement as they were applied during Operation Cast Lead, then it is a smoking gun because it proves the case that Israel was charged with. It proves the main revelations in the Breaking the Silence report. When I read the testimonies in that report – some of which were difficult to read – what was common to them was a change to rules of engagement so that either there were no rules, or they allowed soldiers to shoot anything that moved in the vicinity.

If the quote is true, that means that Israel has abandoned the main safeguard that makes sure that combatants realise the most basic principle of international humanitarian law: the principle of distinction between combatants and civilians. That principle confers a duty to target only combatants and military objects and prohibits the targeting of civilians and civilian objects – unless and for such time as they are actively engaged in hostilities.

Means and intention are the most customary parameters for considering that a person is a combatant or that he or she is engaging directly in hostilities. If you delete them, or even delete one of them, you are providing combatants with a licence to kill civilians.

Leaflets urging civilians to leave an area can be a very positive way of reducing the danger and harm caused to civilians, if there is a no-war zone to which they can go. In Gaza there was no such zone.

Secondly there may always be people who despite the leaflets decide not to leave their homes, perhaps because they have young children or elderly relatives, or perhaps because they have simply decided not to leave their homes, perhaps because they have been refugees before and have vowed that they never will be again.

The laws of armed conflict do not allow the killing of civilians just because they chose not leave their homes which became a war zone.

Of course there is a dilemma for soldiers confronting an unarmed man in civilian clothes who may have some other means of threatening their lives. But that is a risk of combat. International law requires that combatants run risks to reduce harm to civilians.

The principle of distinction is not a suggestion but the product of the experience of the whole of humanity throughout centuries of bloodshed and a means of putting some limitations on warfare as it affects civilians.

The writer is an Israeli human rights lawyer