“We center on one building that confirms where the attack happened, one bomb that shows who carried it out and when, and the victims. The evidence combined exposes Syria’s and Russia’s lies.”

The New York Times, working with the geolocation site Bellingcat and Forensic Architecture, reconstruct the chemical attacks on Douma in East Ghouta, near Syria’s capital Damascus, to establish the Assad regime’s responsibility for the mass killing of about 50 people.

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The Augmented Reality Reconstruction

On the evening of April 7, Syrian military helicopters dropped a chlorine bomb on the rooftop balcony of an apartment building in the opposition-held town of Douma, near Damascus. Dozens of people were sheltering inside as President Bashar al-Assad’s forces waged an intense bombing campaign in a final push to seize control of the rebel enclave.

Chlorine is a heavy gas; it sinks into open spaces and displaces air. In high concentrations, it can be lethal. Chlorine has been used as a weapon so frequently in this war that many Syrians know to move to higher ground and find a source of water when they smell it.

We counted at least 34 victims spread across two floors and in stairways. Many were found near water sources. Our reporting suggests they moved up into the building, not knowing the bomb was on the rooftop, or that they were walking into a death trap. Their bodies showed horrific signs of chemical exposure. A leaked U.N. report, exclusively obtained by The Times, said 49 were killed, including 11 children.

That any chemical attack took place was swiftly denied by Syrian officials and their Russian allies. Proving otherwise became complicated.

The Syrian regime prevailed in its military campaign, seizing control of Douma — and the crime scene. Russian police were the first outsiders allowed to visit the site, followed by Russian reporters, who presented their own version of events: They said the building showed no evidence of a chemical attack, and the bomb on the rooftop balcony was placed there in an attempt to stage the so-called attack.

We were unable to visit Douma. But to get to the truth of what happened, we forensically analyzed the visual evidence unwittingly provided by the Russian reports. Combining those pictures with other videos filmed by Syrian activists, we reconstructed a 3-D model of the building, the balcony and the bomb, in partnership with Goldsmiths, University of London research agency, Forensic Architecture.

The reconstruction brought a virtual crime scene to us. We could inspect how the bomb related to the trove of visual evidence around it, the debris strewn across the balcony, the bomb’s design, the architecture of the rooftop, the damage inscribed on the bomb’s casing, the hole punctured in the roof, and how the bomb penetrated into the room beneath.

Key pieces of evidence indicate that this bomb was not planted, as officials claimed, but dropped from a Syrian military helicopter. The evidence supports chlorine was involved. And it affirmed when it happened — on the evening of April 7, a time frame that is consistent with witness reports and interviews of that day.

New technologies like 3-D modeling in augmented reality and virtual reality offer a new level of remote access and understanding of crime scenes that can benefit human rights investigations. It has been done for more than a decade using satellite imagery and other remote sensing. The specialist groups Forensic Architecture and SITU Research have used these techniques to reconstruct the U.S. bombing of the Al Jinah Mosque in Syria and the shooting of unarmed protesters in Ukraine. Human rights groups have reconstructed the torture rooms in Saydnaya prison. Jurors in the trial of a former SS guard were presented with a virtual reality version of Auschwitz to better understand what the guard would have seen.

Remote access cannot tell us everything, however. Environmental and tissue samples are needed in chemical weapons investigations. But it allows us to perform certain measurements, provide analyses that are less speculative and more mathematical and offer new presentations of critical visual evidence.