On a clear afternoon last Monday a line of humanitarian aid trucks eased to a stop in front of a cluster of warehouses packed with aid supplies 24km outside the Syrian city of Aleppo.
Omar Barakat, director of the local Red Crescent branch, supervised the loading of the 31-vehicle convoy, which was scheduled to drive into the shell-ridden city that evening.
Hours later, Barakat would be dead, his body one of 20 strewn through the convoy's burning wreckage after airstrikes hit the idling trucks. The September 19 attack alongside Aleppo's Highway 60 was the most shocking act of violence in the general collapse of a days-old cease-fire agreement, one of whose key provisions was the unimpeded transit of humanitarian aid into besieged areas of Syria.
"Let me clear: If this callous attack is found to be a deliberate targeting of humanitarians, it would amount to a war crime," UN humanitarian chief Stephen O'Brien said this week.
But what transpired alongside Highway 60 would quickly become obscured in a contest of international finger pointing. Both the Russian and Syrian governments denied striking the convoy and suggested, at different times, that it could have been destroyed in a fire or a ground offensive by terrorists or a strike by a US Predator drone. The United States - just days after mistakenly bombing a Syrian Army position - accused both countries of deliberately targeting the aid and its guardians.
Eyewitness accounts, along with social media postings and video, including footage of the wreckage, added to assessments by US defense officials, show that the convoy was obliterated by airstrikes, first by helicopters dropping barrels loaded with explosives and shrapnel - a long-standing tactic of the Syrian government - and then by Russian bombers.
The convoy had been at the warehouses for hours before the attack and O'Brien said its coordinates were "marked and known" to the Syrian government. Aid workers said the authorities in the capital city of Damascus had also granted the necessary permissions and had been supplied with full details of the convoy's personnel and route.
In addition, a Russian drone observed the trucks as they arrived at the warehouses.
"Around 13:40 . . . the aid convoy successfully reached the destination," Major General Igor Konashenkov, a spokesman for the Russian Defense Ministry said in a statement on Tuesday. "The Russian side did not monitor the convoy after this and its movements were only known by the militants who were in control of the area."
Grainy surveillance footage from the drone, which was broadcast by Russian media, shows a long line of flatbeds and semis angling for parking spots by the Syrian Arab Red Crescent warehouses.
That Monday was a warm fall evening. Ammar al-Selmo, a local rescue worker, was making tea in a building across the street. Stepping onto a balcony just after 7pm, when it already past dusk, he said he listened to a helicopter swoop in and drop two barrel bombs on the convoy.
"It felt like a moment of madness," Selmo said in an interview.
Other testimony suggests a second craft followed in as the first flew off, dropping two more barrel bombs.
Outside the warehouse it seemed everything was burning. Red Crescent staff and volunteers staggered through the wreckage, some of them writhing in flames, Selmo said. And in the lead truck, he said, Barakat was trapped in the cab and screaming for help.
Another rescue worker, who spoke on the condition of anonymity out of fear of retribution, said his team spent just 30 minutes in the wreckage before it heard the roar of approaching jets.
"We just picked up the bodies and ran," he said.
US radar and satellites equipped with thermal sensors detected two distinct heat signatures leaving Russia's Khmeimim air base that evening, a senior defense official said, speaking on the condition of anonymity to discuss intelligence matters. The two Su-24 swing-wing bombers took off and banked northwest, heading for Aleppo. They were the only jets in the area of the convoy, the official said.
He said the US military is confident Syrian helicopters also participated.
The arrival of the bombers was marked by explosions. Videos shot at the scene capture the sound of cannon fire and the low rumble of jets; on the ground, the video shows flame and smoke and captures the sounds of chaos. From his makeshift shelter under an abandoned food truck, Selmo saw the brother of one of the drivers rooted to the spot and sobbing.
From about 8pm until shortly before midnight, the convoy was repeatedly attacked, according to interviews with three rescue workers, including Selmo, who responded to the scene.
"We didn't know where to run or hide because the attacks just kept coming," the second rescue worker said.
Video clips depict a number of distinct strikes while at least one piece of footage posted online includes the distinct rhythmic tapping of a heavy machine gun or aerial cannon, while another - provided by an eyewitness - has the hornlike sound of a jet-mounted chain gun, probably affixed to one of the Russian Su-24s.
Eyewitnesses said the threat of more airstrikes prevented ambulances from reaching the scene for as long as three hours.
The scale of the destruction would not become clear until midnight when the aircraft finally departed, leaving the small contingent of aid workers to assess what was left of their friends and supplies. Eighteen of the trucks were destroyed or damaged, several reduced to twisted metal carcasses, amid a carpet of debris and shredded aid containers.
"We insist on an investigation of what happened on the humanitarian convoy," Russian Foreign Minister Sergei Lavrov said Friday at a news conference in New York. "It's not very difficult to find out what was used to hit it. Artillery shell, rocket, aerial bomb . . . there must be debris left over. We asked the Americans . . . to start an honest investigation. I hope they will do this."
Vehicles and boxes of aid at the site are peppered with shrapnel holes, and pictures, provided by the rescue workers, show at least one distinct crater with the tail fin of an aerially dropped bomb protruding from a box of anti-lice medication. The circular eight-stanchion fin assembly closely resembles that of an OFAB-type bomb.
Open source analysis by research teams at CIT and Bellingcat, two groups dedicated to analyzing photos and information from conflict zones, suggest that the bomb could be an OFAB 250-270, a high-fragmentation weapon designed to destroy exposed equipment and personnel. OFABs are of Russian design and are in use by both the Russian and Syrian air forces.
Other munitions recovered at the scene include what appear to be S-5 aerial rockets. The roughly 4 1/2-foot pencil-looking weapons are often fired from pods mounted on ground-attack aircraft and helicopter gunships.
According to a handwritten ledger kept by the Red Crescent, the youngest victim of Monday's attack was 16-year-old Taqi Hashim. Five of the most grievously injured, including a 14-year-old, are from one family, the Najeebs.
"Tell me what was going through the minds of those pilots?" Selmo asked. "When they bombed an aid convoy, they must have known an ambulance would follow. Why did they wait to kill us? Why did they play this like a video game where you shoot everything that moves."