DOUMA, Syria -- Inspectors finally entered the site of an alleged chemical attack widely believed to be perpetrated by the Russian-backed regime of Syrian President Bashar al-Assad after Moscow delayed their entry for a full two weeks.
Syrian state news agencies falsely reported that inspectors from the Organisation for the Prohibition of Chemical Weapons (OPCW) visited Douma April 17.
In reality, inspectors entered the area April 21 -- two weeks after videos, photographs and the accounts of first responders corroborated claims that a chlorine gas bombardment ravaged the rebel-held enclave.
The April 6-7 attack killed at least 40 people and hospitalised more than 500.
After Russia blocked a number of United Nations measures aimed at identifying the culprits, the United States, France and Britain carried out a widely backed punitive strike against the Syrian regime for its "clear violation" of international law.
What clues might chemical specialists in Syria be looking for?
Despite the long delay, OPCW inspectors could still be able to find chemical traces useful for the probe, specialists have told AFP.
Evidence could be found in the bodies of alleged victims or in the environment near the site.
"Autopsy samples, if available, will provide invaluable evidence," said Alastair Hay, an environmental toxicologist at the University of Leeds.
"Nerve agents like sarin can be present in the environment for many weeks after use and particularly if you look near the site where a weapon has exploded," he told AFP.
Ralf Trapp, a consultant and previous member of an OPCW mission to Syria, said chlorine gas would be harder to find as it would largely have dissipated into the air.
Instead, as chlorine already exists in the environment, investigators might look for unusually high concentrations of the element in materials from the alleged attack site, he said.
"You can erase evidence, but you need to be thorough. And in being thorough, you may well provide clear evidence that the site has been tampered with," Hay said. "Cleaning up a contaminated site would involve the removal of materials that cannot easily be decontaminated."
This "would leave signs that things have been removed, in particular if there is video evidence from the time of the alleged attack" for a comparison, he told AFP.
Even after extensive cleaning, "there is a good chance that deposits of the agents or of their degradation products" would remain, he said, adding that these could be found in materials such as brickwork, concrete and soil.
An independent investigation
The OPCW team "will bring back all the relevant evidence its inspectors find, including of any clean-up or manipulation" at the site of the alleged attack, Trapp said.
The samples will then go to approved independent laboratories around the world. Each sample is split and sent to at least two different labs.
"If the mission cannot demonstrate that chlorine or sarin was used ... at the site, they would present the evidence they have and point to possible scenarios that might explain" it, he said.
It would then "be up to the political organs of the OPCW and to individual states' parties to decide whether the evidence was sufficient to confirm a chemical weapons attack," he said.
The OPCW is mandated with determining whether a chemical weapon was used but not with identifying perpetrators.