Bassam Khabieh / REUTERS A man holds the body of a dead child among bodies of people activists say were killed by nerve gas in the Ghouta region, in the Duma neighbourhood of Damascus, on Aug. 21, 2013.

Early morning Wednesday Syrian anti-regime activists started flooding Twitter with accounts of a missile attack on a rebel-controlled suburb east of Damascus. Then the tweets reported hundreds of casualties, possible victims of an alleged chemical weapons attack. A cascade of amateur videos followed the Tweets, showing scores of dead, but not bloodied, bodies, including those of children, in hospital morgues. Doctors and nurses attended victims with blue lips and pink blotches on their skin. Volunteers attempted to resuscitate victims who had stopped breathing, and in other videos men, women and children convulsed or foamed at the mouth (Warning: these videos, collected by well known weapons expert and blogger Brown Moses, contain graphic scenes of death and nudity).

The local medical committees of Jobar and Ain Tarma, the suburbs near where the alleged attack occurred, sent out an urgent appeal. “The disaster is huge, we are out of all kind of medicines, we have used all our stocks from cortisone and atropine.” They said they had administered 25,000 injections of atropine, which is used for resuscitation and as a treatment for nerve gas poisoning.

International condemnation was immediate. Britain said that if confirmed, the use of chemical weapons in Syria would be a “shocking escalation,” according to Reuters. Foreign Secretary William Hague said the UK would raise the issue at the UN Security Council. The Arab League urged the UN, whose chemical weapons inspectors arrived in Syria this week, to inspect the site immediately. In Damascus, the pro-regime Harsta News Network, with more than 12,000 Facebook followers, crowed in triumph. “Finally the Syrian chemicals have been launched,” the administrators wrote. “By the orders of President Bashar Assad….Today at 05.30 in the morning, East Ghouta was targeted with Asadi Chemical weapons and the operation was successfully accomplished. we wait for a detailed summary from our valiant troops to be issued within few hours.” An hour later the post was deleted (it can be found cached on Google), but not before the post got 69 “likes” and the poster re-commented: “Soon Bashar will not only be the ruler of Syria, he be will the ruler of all the Arab world and the chemical weapons are coming for you scumbags.”

Still, it’s hard to imagine that the Syrian government would be so foolish as to fire chemical weapons on the outskirts of Damascus, three days after the arrival of a UN team tasked with investigating three other incidents of alleged chemical weapons attacks that took place six months ago. Syrian state TV denounced the allegations, saying , “the news broadcasted by some media outlets that chemical weapons have been used in Eastern Ghouta (suburbs) is untrue and baseless…the aim behind broadcasting such reports is to distract the UN investigators away from their mission.”

But what else could the footage be? Even on evidence-based forums dedicated to parsing the facts, accusations flew between pro-and anti-regime supporters: It’s a propaganda ploy by rebels eager to get attention now that investigators finally are in Syria. It’s a sign of Assad’s blithe indifference to international condemnation. Either way the conspiracy theories defy logic – faking footage like that would be a Hollywood-size undertaking, and the repercussions of exposure would be fatal for a movement that has already been tarred by its associations with al-Qaeda and other Islamist jihadi groups. For Assad to launch such an attack now would be a raised middle finger to the international community; a confirmed attack would surely result in staunch ally Russia, as a signatory to the International Convention against Chemical Weapons, reconsidering its support for the regime.

The number of dead – now said by opposition activists to number at least 213 (conditions on the ground have made independent verification impossible) – is far more consistent with a chemical weapons strike than previous alleged attacks that resulted in just a few dozen casualties. But the evidence presented in the videos is still inconclusive, says toxicologist Ralf Trapp, an independent consultant on chemical and biological weapons disarmament who has been following the issue of Syrian chemical weapons closely. “[These videos] appear to show a lot of victims, people are vomiting, they have breathing problems, and there are significant dead. It all looks like it could be an attack with a chemical warfare agent, but it’s impossible to rule out other possible causes.”

Trapp has seen little of the dilated pupils, contortions and massive muscle paralysis that would indicate a powerful nerve agent such as sarin, but that could be due to the bad video quality and amateur footage taken under difficult conditions. Some of the symptoms, such as foaming at the mouth, could point to chlorine gas or some other agent that attacks the lungs. It’s also possible that the victims are suffering from massive oxygen deprivation brought on by the detonation of a fuel explosive in the air just above the attack site that consumes large amounts of oxygen when it ignites. Or, he says, a chemical weapons depot could have been hit by a rocket, releasing agents into the air.

One worrying sign, says Trapp, is the large number of child victims. “That is consistent with a gas or attack on a congested urban area inhabited by families.” The only way to know for sure is to send investigators to the scene immediately. “This is the moment for the UN team to go to the scene. They can inspect the site and do tests, they can talk to victims, and they can analyze blood and tissue samples for traces of nerve agent.” The question is whether or not they can get access to the site. Swedish scientist Ake Sellstrom, who is in Damascus heading up the UN chemical weapons inspector team there, told TT news agency by telephone that while he had only seen TV footage, the details sounded suspicious, according to Reuters. “It sounds like something that should be looked into.” If a request is lodged with the Secretary General of the UN, he said, “we are in place.” But getting to the site may not be easy. It is under rebel control, and the government—if it is willing to allow the team access— is unlikely to be able to offer a guarantee of safety. Even if the UN team does manage to visit the site to conduct a conclusive investigation, it will not, by its mandate, be able to assign blame. If the team can’t access the site, it can still interview doctors and victims if the government allows to understand better what happened, says Trapp. If they can’t do either? “Denial of access to the site, or to the doctors and victims, shouldn’t be taken as proof that there was a chemical attack by the regime. But it could be an important indicator.”

—with reporting by Rami Ayesha / Beirut