GEORGE OURFALIAN / REUTERS In this March 23, 2013 photo, animal carcasses lie on the ground, killed by what residents said was a chemical weapon attack on March 19, 2013 in the Khan al-Assal area near the northern city of Aleppo, Syria.

Updated April 13, 2013

One witness said he smelled chlorine. Another remembered the scent of rotting garbage. There were photos of dead farm animals in a yard, and video footage of survivors struggling to breathe. But of the 31 casualties of what the Syrian government has labeled the opposition’s first chemical weapons attack, on March 19, there is no list of names of the deceased and no footage of coffins that can be directly attributed to the incident. Immediately following the alleged attack, the Syrian government demanded an international investigation, and the U.N. Security Council obliged, scrambling a team with the assistance of the Organization for the Prohibition of Chemical Weapons (OPCW). Nearly a month after the attack, that team is twiddling its thumbs in Cyprus, waiting for a green light to enter Syria even as the evidence, whatever is left of it, evaporates into thin air.

(MORE: The mystery behind a chemical weapons attack in Syria.)

Discussions on the proposed investigation between the government of Syrian President Bashar Assad and the U.N. remain deadlocked. The Syrian government requested only an inquest into the one attack on a pro-regime village just outside of Aleppo last month. The rebels, too, want an investigation. They hold that they were framed by the government, and believe that an international investigation will exonerate them. But they have also raised the issue of two other alleged chemical weapons attacks, one in Damascus in March and another in Homs in December. Both the rebels and the regime have traded accusations over all three events. The U.N., responding to pressure from France and the U.K., insists that the investigators have access to all three sites, something the Syrian government is refusing to grant upfront. According to Reuters, an April 6 letter from Syria’s foreign minister to the UN.. said that access to Homs would be granted only after the investigators went to Aleppo, and then only once the mission’s “honesty and neutrality and the credibility of its work away from politicization” was ascertained. The U.N. is unlikely to comply with such conditionality.

Without a site visit, it would be impossible to conduct an investigation, says Dr. Jean Pascal Zanders, a chemical weapons expert at the EU Institute for Security Studies in Paris. Blood samples could be taken from victims who survived a low dose, if they were able to leave the country. But even then it would be circumstantial evidence. “How do we know that person was at that site, at that time? Without corroborating evidence, there is no proof,” he says.

Syria has never confirmed or denied possessing chemical weapons, though intelligence estimates from multiple countries, as well as the OPCW, hold that they have one of the biggest stockpiles in the world. In July, the Syrian foreign ministry spokesman stated that the government would only use chemical weapons in case of a foreign attack, and never against its own people, the closest the country has come to acknowledging the existence of chemical stockpiles in the country. Syrian ambassador to Lebanon Ali Abdul Karim Ali, in a recent conversation with TIME, suggested that the weapons could be used defensively within the country, say, against a brigade of foreign fighters. “I don’t know if Syria has chemical weapons. But I do know that we will not hesitate to defend ourselves with all possible means, to the maximum capacity, if any of our territory is breached,” Ali says.

To Zanders, such rhetoric is the equivalent of cold-war nuclear brinksmanship, implying the presence of weapons of mass destruction to counter Israel’s unconfirmed nuclear arsenal: “My personal assessment of Syria’s arsenal is that it is a weapon of last resort. Not something to be used on the battlefield, but as a strategic weapon.” Syria’s chemical weapons, he says, “are unsuitable for the type of civil war combat that we are seeing now,” something the regime is likely to take into consideration. Zanders, like many other chemical weapons experts, is under the impression that none of the three attacks in question involved banned chemical weapons like Sarin, VX or mustard gas, based on evidence available via YouTube. Chlorine gas, or riot control substances such as pepper spray and CS tear gas may have been used in lethal dosages, but those are not banned outright under the Chemical Weapons Convention.

UPDATE: Riot control substances, such as pepper spray and CS gas are permitted under the convention as long as they are used purely as a law enforcement measure, adds Zanders. However, “If the same agent is used by military forces in combat, as might have been the case in Syria, then it is absolutely banned, and would trigger all the consequences of the Chemical Weapons Convention.” The same would apply to the use of chlorine as a weapon of war. Which is why it is so important to find out what, if anything, was used at these three sites in Syria.

Still, the fact that there has been no clear evidence of chemical weapons use two years into the war is a good sign, says Zanders. “Everyone is focused on the doomsday scenario, but what is significant now is what is not happening, and my assessment is that chemical weapons have not been used.”

Of course, the lack of proof one way or the other makes it difficult to breathe easy. Which is why the investigators are still waiting in Cyprus, despite a month having elapsed since the alleged attacks and the growing prospect that evidence has disappeared. Syria and the UN are in a stalemate. It will be difficult for the Assad regime to back away from its demands, as they have already reached the highest levels of the UN. “There will be consequences if the investigation doesn’t go ahead,” says Zanders. “The next time the UN Secretary General endorses such a request, he will first discuss the parameters, so that the mandate is clear from the start.” It’s probably too much to hope that there won’t be a next time.