On the night of January 9, 2009, the Salha family were sleeping, and Gaza was under attack. They were woken by a loud bang at 3am: a missile, fired at the house, entered through the roof, and landed in one of the rooms. What the family did not know was that this was a warning. From that moment of impact, they had just three minutes before the house would be destroyed.

After moments of terrified confusion they began to leave. A first group managed to escape but as the second group reached the bottom of the stairs, a bomb struck the building, killing six of them: Randa, 34; Fatma, 22; Diya, 13; Rana, 12; Baha, 7; and Rola, 1.

These are the findings of an investigation, one of several produced for a UN inquiry into drone strikes by Forensic Architecture - a project based at the Centre for Research Architecture at Goldsmiths, University of London. We interviewed the surviving members of the Salha family in Gaza by satellite link from Al Jazeera's London offices, and built a 3D computer model of their home with them. Our work was an attempt to reconstruct what happened between the warning shot and the lethal shot. The architectural model provided an aid for the recollection of events obscured by time and trauma. It was evidence intended to counter the Israeli Army's version of the event and the legitimacy of its "lawfare".

In fact, Israel has been using warning tactics for many years. They started as phoned-through messages, informing people that they had minutes to collect their belongings and vacate the building before it was bombed. Finding that they couldn't always get through, however, the Israeli Army began to use so called "roof knock" strikes. These involve the firing of a low- or non-explosive missile - usually from a drone - at the roof of a building that is to be destroyed. A bomb that devastates the building follows the missile a short time later.

Five years later, neither the tactics, nor the consequences have changed. Since the ongoing offensive on Gaza began, human rights groups in the strip have reported one warning shot that resulted in the death of a six-year-old child, Abdel Rahman Khattab, in Bouba, on July 10; another attack, on the home of Odeh Ahmad Mohammed Kaware, where a warning missile was followed by a bomb that killed seven people, including five children. In another incident, a warning missile injured two women and an infant in Rafah.

Having run out of distinct government buildings or pieces of military infrastructure to bomb, the majority of what Israel is now targeting in Gaza are civilian homes - and the bodies are piling up. Israeli spokespersons, anxious to present themselves as seeking to minimise civilian casualties and as acting within the bounds of international law, now repeatedly explain that the Israeli Army gives warning before it attacks civilian buildings. But it is the warnings that allow the Israeli Army to attack them at all, and the warnings that are now responsible for the mounting death rate.

Israeli military lawyers argue that if residents are warned, and do not evacuate, then they can be considered legitimate collateral damage. Under this interpretation of the law, the civilian victims become human shields. This is a gross misuse of international law. It is illegal to fire at civilians, even if the intention is to warn them. It is ridiculous to ask them to understand, in the commotion and chaos of war, that being shot at is a warning - and it is outrageous to claim that this is undertaken to save their lives.

International law should protect civilians. In Gaza, it is being abused in order to enable attacks where attacks should not be undertaken at all.

Very often both journalists and commentators - even those sympathetic to the Palestinian plight - are lost for words when asked to explain what is wrong with warnings. Would you rather, the Israeli Army insinuates, that it uses no warnings at all? How, after critiquing indiscriminate and inaccurate strikes, to protest tactics whose entire logic is to be more precise in choosing between perpetrators and bystanders?

To be asked to choose the lesser evil from a limited set of choices is a fallacy. Those posing lesser-evil dilemmas are always those in power and the problem is always concerned with the death and fate of others.

At the Salha family home there was no weapon cache, no militant headquarters. The Israeli Army simply made a mistake, and later admitted as such. Yet when the few surviving members of the Salha family petitioned the Israeli court for compensation, their case was curtly dismissed. The judge explained that Israel was not liable to consequences resulting from an act of war, and ordered the Salha family to pay the court the costs incurred in bringing the case.

Today in Gaza, the combination of the technology of precision strikes with the legal tactics of warning allows the expansion of the depleted bank of targets and the proliferation of violence. From the air, Israel has started destroying - after warnings of course - not only places it claims are weapon caches but also the houses of Hamas' field command. Now the target list seems to have extended even to include attacks on hospitals. On July 11, four warning missiles were fired at the Al Wafaa hospital, close to the Israeli border.

With this combination, the Israeli Army has found a tool to enable it to strike targets it should not be striking at all - targets of little military effect, in built-up areas that house many civilians. Since it now has such a tool, the Israeli Army will go on using it until somebody forces them to stop. Confronting Israeli tactics of warning is now a matter of utmost urgency.

Eyal Weizman's work on drone strikes, Forensic Architecture, and the architecture of the Israeli occupation are featured in the documentary The Architecture of Violence, as part of the upcoming Rebel Architecture series.

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