Abdulhamid al-Youssef sobbed as he carried his infant twins, wrapped in matching white shrouds, to their final resting place.
Ahmad and Aya, nine months old, died on Tuesday morning in a chemical attack on the town of Khan Sheikhoun in Idlib, northern Syria, along with Mr Youssef’s wife Dalal and 16 other members of his family.
On Wednesday he had to bury them all in an unmarked mass grave.
The 29-year-old supermarket cashier had been at work when the air strike hit close to his home just after 6.30am. When his wife called to tell him what had happened, he rushed home to be with them.
They appeared to be fine, but as a precaution he took them all down to the basement of a nearby building in case of another strike.
It was only then, an hour later, that they began displaying symptoms.
“The family was all waiting down there and were safe, but then they started choking,” Mr Youssef’s cousin, Alaa, told the Telegraph. “The twins suddenly began shaking and struggling to breathe. Then he watched the chemicals take hold of his wife, then his brother, nieces and nephews.
“Everyone died down there in the basement, they didn’t have time to get to the hospital.”
Chemical attacks leave no marks. It’s a silent killer that works its way through the body slowly
Dr Mamoun Najem
Mr Youssef held his children – who looked peaceful in death – in a tight embrace, one last time before laying them into the ground. Apart from a bruise on Ahmad’s cheek there were no obvious signs of injuries.
“Chemical attacks leave no marks,” said Dr Mamoun Najem, a doctor at al-Rahma hospital in Idlib who treated the victims. “It’s a silent killer that works its way through the body slowly.”
He saw dozens of patients arrive that morning and into the afternoon. He says he has never seen such severe cases of poisoning before.
“Their pupils were as small as pinpricks, their skin was cold. They were unresponsive like zombies,” he said.
A nurse at the hospital, who did not wish to give his name, said: “The smell reached us here in the centre; it smelled like rotten food. We've received victims of chlorine before - this was completely different.
“Victims had vomit from the nose and mouth, a dark yellow colour, sometimes turning to brown. They had paralysis of their respiratory functions - children were dying faster than adults because of this.”
Footage of the aftermath of the attack shows victims convulsing, struggling to breathe, and foaming from the mouth.
Idlib governorate’s medical authority released an updated list of the dead on Wednesday. The youngest of the Youssef family was nine months old, the eldest was 68.
The death toll has reached 73, 23 of whom children, making it the deadliest chemical assault since 2013, when the Syrian government dropped sarin on a suburb of Damascus suburbs, killing hundreds of people as they slept.
The number was expected to rise further, however, as many are believed to died in their homes and are yet to be taken to the hospitals to be counted.
Their pupils were as small as pinpricks, their skin was cold. They were unresponsive like zombies
Dr Mamoun Najem
The World Health Organisation (WHO) said on Wednesday the symptoms victims displayed were consistent with exposure to a category of chemicals that includes nerve agents.
“The likelihood of exposure to a chemical attack is amplified by an apparent lack of external injuries reported in cases showing a rapid onset of similar symptoms, including acute respiratory distress as the main cause of death,” it said.
Neither side denied there had been a chemical attack, however Russia claimed a Syrian government air strike had hit a rebel chemical weapons warehouse, while the US and UK pointed the finger solely at President Bashar al-Assad’s regime.
Hasan Haj Ali, a senior rebel commander, called the Russian assertion “a lie,” saying the rebels did not have the capabilities to produce chemical weapons and there were no military positions in the area bombed, either.
The Telegraph spoke to witnesses on the ground in an attempt to reconstruct Tuesday’s events.
The attack happened around 6.32am local time. A video distributed by opposition activists claiming to be of the moments after the air strike, which hit Corniche Street in a northern neighbourhood of Khan Sheikhoun, showed several large plumes of smoke.
“The sound of the explosion was not what we are used to - I thought that this one hadn’t exploded, because of the thump sound it made, not an explosion sound,” one witness said.
Alaa al-Youssef said he heard planes circling above before they dropped their load 300ft away. The wind had been blowing west and away from Mr Youssef’s house, but had it not been he believes he would almost certainly be dead.
He said some time after he then went over to investigate the scene, where he saw a rocket that had failed to explode. “I saw black liquid oozing out of the casing,” he said. “We have been hit by many rockets before but I’d never seen anything like this.”
It was not immediately clear to residents that the attack was chemical in nature as the symptoms did not start until some time after.
When White Helmets civil defence workers made it to the area an hour later they went door-to-door checking for survivors, but instead found whole families dead in their beds.
Those still alive were taken to al-Rahma hospital, which had been hit two days earlier in a regime air strike and as a result was struggling to deal with the hundreds of patients they were seeing.
Then, as medics were treating those wounded in Tuesday’s attack the hospital was targeted again by rockets, killing one patient and putting the clinic out of service.
The regime says it has no reason to attack Khan Sheikoun, which is seven miles from the nearest frontline. Its opponents say the same.
Experts say it is doubtful that rebels had the finances or materials to manufacture the toxic substance, and have been able to do so without attracting attention.
“Even assuming that large quantities of both sarin precursors were located in the same part of the same warehouse (a practice that seems odd), an air strike is not going to cause the production of large quantities of sarin,” said Dan Kaszeta, a former US Army Chemical Corps officer who has worked in chemical defence issues for over 25 years.
To date, all of the nerve agents used in the Syrian conflict have been binary chemical warfare agents, so-named because they are mixed from several different components.
“Dropping a bomb on the binary components does not actually provide the correct mechanism for making the nerve agent,” he said.
And, unlike the regime, rebels are not known to have used sarin gas in any attack to date.
Suspicions have remained that a portion of the Syrian government’s sarin stockpile was not declared to UN inspectors, who supervised the surrender of its supplies in 2014.
“There are no warehouses, no factories anywhere in Khan Sheikoun,” Mr Youssef told the Telegraph. “There aren’t even any fighters, just civilians who are trying to survive.
"The opposition would never bomb its own people,” he said.