A painstaking reconstruction of a series of Israeli airstrikes that killed two Palestinian boys on the roof of a building in Gaza City this summer suggests that Israel’s military tampered with its own surveillance footage of the attack, possibly to conceal evidence that the children were visible to the drone pilots who carried out what were supposed to be nonlethal “warning strikes.”

The visual investigation of the July 14 killing of Luai Kahil and Amir al-Nimra , both 14, was carried out by Forensic Architecture , a research group based in London that works with communities affected by state violence (and has previously partnered with The Intercept), and B’Tselem , an Israeli human rights group that documents Israel’s abuses in the occupied Palestinian territories it has controlled since 1967.

Forensic Architecture created a detailed visual timeline of the incident, which offers compelling evidence that a video report shared on Twitter by the Israel Defense Forces in the immediate aftermath of the attack distorted the sequence of strikes to give the false impression that the roof was unoccupied when the missile that killed the boys was fired.

Moments ago, IDF fighter jets struck a high-rise building in the Al-Shati refugee camp in northern Gaza. The building was a Hamas training facility. A tunnel was dug under the building & used for underground warfare training. This tunnel is part of a Hamas terror tunnel network pic.twitter.com/M3C53RKMaC

Using open-source visual evidence — including a rooftop selfie taken by the boys shortly before the airstrike that killed them, timestamped security camera footage of the sequence of Israeli strikes, witness video of the mangled bodies of the two boys after they had been torn apart by shrapnel from what Israel described as the first in a series of four “warning strikes,” and a YouTube cooking video recorded by three children in a nearby kitchen during the attack — Forensic Architecture concluded that the Israeli army had misleadingly substituted footage of the third missile strike for what it described as the first impact, which had killed the boys.

Why did @IDF take the trouble to switch the clips around? Were Luai Kahil and Amir a-Nimrah visible in the missing clip? It's unlikely we'll ever know - though people are visible in footage of the other strikes. pic.twitter.com/Iv7aLNGJuf

According to the investigators — who also relied on witness testimony, local news footage, and an architectural model of the destroyed building in Gaza City’s al-Katiba Square — by the time the third strike hit the building, nine minutes after the first missile, the bodies of the boys had already been evacuated from the roof.

Eyal Weizman, the Israeli architect who founded Forensic Architecture and was the principal investigator of the strike that killed the two boys, argues that Israel’s own video of the incident proves that the army’s entire concept of warning strikes is flawed. “In a city like Gaza, subject to so many attacks, of so many different types, it is unreasonable to expect civilians to become munitions experts, and to understand that a small missile is a message rather than the normal attempt to kill and destroy,” Weizman wrote in an email to The Intercept on Wednesday. “We can see in this case a demonstration of this misunderstanding. When the first responders ran to the roof to evacuate the teens after the first strike, it was likely because they did not understand that this was a warning, as they wouldn’t run onto the roof of a building about to be demolished.”

Hagai El-Ad, executive director of B’Tselem, told The Intercept that the video posted on Twitter by the Israeli army, along with the boast that the attack demonstrated “the IDF’s intelligence and operational capabilities, which will become deeper and stronger as necessary,” aroused suspicions from the start, since it seemed to include surveillance footage of all four initial strikes but showed no trace of the two teenage boys killed by the first blast.

“We knew from the outset, from our field research, from testimonies we collected, as well as from social media, that Amir and Luai were on the roof of the building when they were killed. They were in plain sight, in broad daylight, on a large, empty roof — in principle, as exposed to aerial surveillance as one could be. Yet in the video footage released by the Israeli army, they are not seen. This was very difficult to reconcile, so it was important for us to try and not leave this unanswered,” El-Ad explained in an email.

“Through the expertise of Forensic Architecture,” he added, “it was possible, step by step, to understand what happened on July 14, including how the Israeli army omitted the first ‘warning’ strike — the lethal one which killed the two teens — from the video it released, replacing it with footage of the third strike, shot from a different camera.”

Since actual footage of the first strike seems to have been concealed by the Israeli army, Amit Gilutz, a B’Tselem spokesperson, said in a statement that “we don’t know if the boys were visible to the military before the first strike.” As The Intercept reported earlier this year, however, Israel’s military has repeatedly claimed that its surveillance drones give remote operators the ability to call off airstrikes when they detect the presence of civilians near targets intended for destruction.

In this case, since other figures — the bystanders who rushed to the roof to try to save the boys — were clearly visible in surveillance video of the second strike, the Forensic Architecture investigators are convinced that the two boys should have been visible in the unreleased footage.

After the Israeli military said in a statement on Tuesday that the Forensic Architecture video report was the first visual evidence it had seen of the two boys’ presence on the roof, the researchers responded by daring the army to produce the surveillance footage of the first strike. The investigators tweeted at the Israeli military: “share with us the footage of the first warning strike to hit the Katibah building on 14 July 2018, and we’ll show you Luai and Amir.”

The Forensic Architecture timeline also suggests that an Israeli military spokesperson, Lt. Col. Jonathan Conricus, lied to the New York Times on the day of the attack, when he claimed that the first four smaller-scale strikes, intended to warn civilians to evacuate the area, were fired more than an hour before the building was blown up. According to the security camera footage obtained by Forensic Architecture, a high-intensity missile was fired at the building at 6:02 p.m. that day, less than 17 minutes after the first warning strike that killed the boys.

Nonetheless, the perception that Israel takes extraordinary measures to warn Palestinian civilians to evacuate before dangerous bombing begins in Gaza is widespread among Israelis. Just hours after the boys were killed on July 14, an Israeli civilian in the nearby town of Sderot, Refael Yifrah, complained in a radio interview that she had been warned by the local civil defense authorities to take cover just seconds before an incoming missile fired from Gaza exploded at around 6:15 p.m. “It’s better to be in Gaza where they get warning that they’re going to be fired upon in one neighborhood or another and they evacuate,” Yifrah said. “Here, there’s an alert, no one knows where it’s going to land.”

Eyal Weizman has long contested Israel’s claim that firing warning shots to encourage civilians to evacuate is permissible under international humanitarian law.

“Israel has been using warning tactics for many years,” Weizman wrote during Israel’s aerial bombardment of Gaza in 2014. “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.”

“Israeli military lawyers argue that if residents are warned, and do not evacuate, then they can be considered legitimate collateral damage,” he added. “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.”

Weizman’s team noted in its report on the killing of the Palestinian boys this summer that video recorded by witnesses who rushed to evacuate Luai and Amir after the first strike showed a fragmentation pattern on the roof identified by weapons experts as “consistent with the explosion of a munition loaded with shrapnel — specifically designed as a lethal weapon.”

“The fact that they shoot munitions of enhanced lethality” in the guise of warning shots “is outrageous,” Weizman said in a recent interview with The Intercept in London. “It’s not even just like a kind of standard explosive,” he added. “They say that a warning strike should be noisy only … like a firework, but the design of that is to tear through flesh. If you look at the catalogues, the way they describe those fragmentation shrapnel sleeves is exactly to increase the lethality of those strikes.”

His team’s reconstruction of what happened in Gaza was “very much a way of honoring two lives that have been lost,” Weizman added, but also a way to draw attention to Israel’s policy on warning strikes. “It’s so important because the issue of warning shots is exactly exemplifying the entire paradox of Israel’s self-perception as a humanitarian party or the most moral army in the world,” Weizman said.