But one thing was missing: the weapons inspectors who arrived in Syria last week to establish what really happened in Douma.
Six days later, they are still demanding full and secure access to the site, a delay that has sharpened suspicions among local residents and Western governments that Syrian and Russian authorities are using each day that passes for a coverup.
People present in Douma said Syrian and Russian military officials have blocked off and repeatedly entered the sites and medical facilities that the international Organization for the Prohibition of Chemical Weapons (OPCW) is expected to comb for evidence.
On Thursday, the United States said it had credible information to suggest that Syria and Russia were working to delay the OPCW mission to Douma as their forces removed evidence that a chemical attack had taken place.
“Russian officials have worked with the Syrian regime, we believe, to sanitize the locations of the suspected attacks and remove incriminating evidence of chemical weapons use,” said Heather Nauert, spokeswoman for the State Department.
Witnesses described a smell of chlorine in the air, and video footage from the site of the deadliest strike showed men, women and children who appeared to have died foaming at the mouth, a symptom that could indicate exposure to a nerve agent.
Assad’s government denies using chemical weapons, and Russia has offered competing explanations for the chaotic scenes of April 7, first denying that an attack took place, then saying it had been staged by rebels.
“In these international investigations, you find a whole bunch of stakeholders who have significant power but might not want the truth to come out, or they may want their version of the truth to come out,” said Jerry Smith, a risk consultant who participated in earlier OPCW missions to Syria.
As inspectors continue to demand access to Douma, the likelihood that they will be able to detect chemical traces is diminishing by the day, according to experts.
Alastair W.M. Hay, a toxicologist and professor at the University of Leeds, said that chlorine was likely to have vanished from the site and that any traces found in the biomedical samples of victims were likely to be inconclusive because chlorine appears naturally in the body.
Remnants of a nerve agent also would be increasingly difficult to find, he said, although they could be detectable in the samples of living victims or exhumed bodies.
“It could also still be stuck in the walls or on nearby rocks, as long as there was no attempt to try and remove them,” he said.
Residents say they worry that Syrian authorities and their Russian allies are whitewashing the history of April 7.
“They asked us not to talk about anything. There was a direct warning,” said a man who said his sister died in the attack and who spoke on the condition of anonymity out of fear for his safety. “Evidence has been erased. There is no evidence.”
Days after the Syrian government reestablished its hold on the area, doctors appeared on state media outlets denying the attack had taken place.
In interviews with The Washington Post, residents confirmed that the doctors were present in medical facilities on the night of the alleged chemical attacks. The residents noted that these doctors were later questioned by security officials, and several people, who indicated that those exchanges were described to them, said the doctors were pressured into publicly denying that an attack occurred.
Several residents said the doctors initially were treated well, even being offered a meal with a Syrian security official before they were told to deny the attack on camera.
Then the pressure increased. Ghanem Tayara, director of the Union of Medical Care and Relief Organizations, a group that operated in the area, said the doctors were interrogated one by one and efforts were made to ensure they had not hidden any biomedical samples.
“Their houses have been raided by police and regime forces who have checked carefully to make sure no one has hidden any samples. Their phones have been checked for any messages suggesting that there was a chemical attack, and even their families have been interrogated,” he said.