Beirut - The early-morning barrage against rebel-held areas around the Syrian capital immediately seemed different this time: The rockets made a strange, whistling noise.
Seconds after one hit near his home west of Damascus, Qusai Zakarya says, he couldn't breathe, and he desperately punched himself in the chest to get air.
Meanwhile, in rebel-held areas east of Damascus, hundreds of suffocating, twitching victims were flooding into makeshift hospitals following a similar rocket barrage. Others were later found dead in their homes, towels still on their faces from their last moments trying to protect themselves.
In a series of interviews with The Associated Press after the suspected poison-gas attack on 21 August, witnesses, survivors and doctors described scenes of horror they say will haunt them forever.
Activists and the group Doctors Without Borders say at least 355 people died in the attack that has provoked international condemnation and shocked a world that had grown largely numb to the carnage of Syria's civil war, which has killed more than 100 000 people in 2½ years. Fuelling the outrage were online videos that showed scores of children killed in the attack.
Convinced that President Bashar Assad's regime was responsible for the attack - a charge Syrian officials strongly deny - the US and its allies are now hurtling toward military action, though they have not yet presented concrete proof.
UN chemical weapons experts this week took biological samples from several victims - a step US officials said came too late. But they are not seeking to answer the question of who was responsible for the attack, just whether chemical agents were involved.
Witnesses interviewed by the AP say they can't prove it but believe government forces were responsible, saying that it is consistent with the nature of Assad's regime and that nobody else had the capability to fire such weapons.
The US administration, meanwhile, is said to be preparing a report for key members of Congress laying out the evidence against the Assad government. A declassified version was to be released to the public, but so far that has not happened.
"To suggest that the rebels did it is simply ridiculous. ... Why would they hit themselves with chemicals?" asked Ammar, a resident who said he miraculously survived the barrage on Moadamiyeh, where 80 people were killed. He declined to give his full name because he was afraid for his life.
The rocket assaults came around the same time on two suburbs on opposite sides of the capital: Moadamiyeh to the west and several districts to the east, including Zamalka, Ein Tarma and Arbeen. The two areas are around 15km apart.
Ammar said he was awakened by shelling around 05:00, just before dawn prayers, when he heard a screeching sound unlike anything he had heard before, followed by the sound of people screaming on Rawda street below his apartment. Once outside, he said, he saw a gas with a faint green color. It "stung my eyes like needles."
"I ran out to see what was going on and saw people in various stages of suffocation and convulsions. I tried to help, but then my legs buckled and I fell to the ground," he said.
Ammar woke up at a makeshift hospital, previously a Red Crescent centre, where he said he spent five days getting water, oxygen and injections of atropine, which can be used to counteract the effects of nerve gases.
A week later, Ammar said he has not fully recovered. He suffers bouts of cold sweats, exhaustion, hallucinations and a runny nose. Worst of all, he said, were the nightmares.
"I can't sleep anymore. I keep seeing the people who died, the scenes from the hospital of people twitching and foaming. I can never forget that," said Ammar, aged 30, who worked in the clothing business before the war and now is a government opponent who sometimes deals with the media.
His father, who identified himself by his nickname, Abu Ammar (Arabic for Father of Ammar), was at the nearby al-Rawda mosque along with a small group of people waiting for dawn prayers when the first rockets hit. He said some people ran outside and then came back in immediately, shouting, "Chemicals! Chemicals!"
He put water on a tissue and covered his mouth and nose, and then went out.
"I saw at least seven people lying on their backs, completely still," he said.
Zakarya said the rockets crashed with a strange whistle "like a siren." Friends took him to the hospital, where he saw dozens of people crowding the rooms and corridors, many of them in their underwear as nurses and doctors doused them with water. That was when he fainted.
When he came to, doctors were injecting him with atropine and he started vomiting. "Strange colours came out of my stomach," the man said. He fainted again and later woke up in the street outside in his underwear, apparently moved out to make room for others.
Later, he felt well enough to go home and said he slept for 13 hours. "When I woke up I felt like Alice in Wonderland," he said. "Everything looked distorted and I couldn't remember anything."
"My eyes felt as if they were on fire, and every time I tried to smell something I felt terrible pain. My chest also ached," he said, his speech interrupted by a hacking cough that he said was one of the lingering effects of the gas.
To the east of Damascus, some 600 patients poured into a makeshift hospital in the district of Arbeen, most of them from the nearby Zamalka area, said Abu Akram, a 32-year-old doctor at the facility. Of those, 125 died, including 35 children, he said.
He said the signs - twitching, foaming at the mouth and nose, constricted pupils - were all clear signs of a kind of nerve gas.
Most of the first arrivals were alive, he said. They were stripped down to their underwear, and doctors poured water on them to avoid contamination. Late arrivals who had been exposed to the gas for a longer time, he said, came in dead. Many of them were children.
"They have a much smaller and weaker respiratory system," he explained.
Abu Akram said he was told by several medics that some people were found in their homes, with wet towels on their faces or hiding with their children in bathrooms.
"People didn't die in their sleep; they tried to save themselves," he said, speaking from the eastern suburb of Arbeen, via Skype.
Mergo Terzian, president of Doctors Without Borders, told AP this week that chemical weapons specialists working with the Paris-based group reviewed the photos and videos and said the symptoms - no sign of trauma, dark patches on the skin, problems breathing - were consistent with a poison gas attack.
Doctors Without Borders, which provides assistance to several clinics in the area, said the medical staff in one of the facilities reported that 70 out of 100 volunteers suffered symptoms after direct contact with patients, and that one died. Several doctors at the facility suffered blurred vision, loss of consciousness, general body pains and watery eyes, the group said.
Amy Smithson, a senior fellow at the James Martin Centre for Nonproliferation, also said the symptoms appear consistent with a nerve gas agent, such as sarin or VX.
Experts say it is very difficult at this point to know definitively who was behind the attack. But Smithson said one of the reasons Washington and London appear so convinced it was the regime has to do with the nature of these attacks: multiple rockets fired in the early hours of the morning, when low winds and temperatures would help the gas stay on target.
Assad defenders, however, question why the regime would carry out a chemical weapons attack just as UN inspectors had arrived in the country, and when the military seemed to have the upper hand in the fighting on the ground.
The government has accused foreign fighters among the rebels of carrying out the attack. While the rebels are not known to have chemical weapons or the ability to deploy them, government supporters say intelligence agencies belonging to countries backing the rebellion could have delivered such weapons to rebels along with the know-how in a bid to frame the regime.
"This reeks of Iraq," said Fathi, a shop owner in Damascus, echoing Syrian Foreign Minister Walid al-Moallem, who a day earlier likened the Western allegations to false American charges in 2003 that Iraq possessed weapons of mass destruction before the US-led invasion of that country.
"How can they be so sure that the regime was behind this attack? Where's the proof? Why the accusation before the UN has had a chance to investigate?" he asked, declining to give his full name for fear of retribution.
"I fear someone did this to frame the regime, leading up to US military intervention."