What can UN investigators find in Syria?

The UN said it will take about two weeks to investigate the alleged chemical attacks on Syrian civilians [EPA]

 Al jazeera -- The delay in accessing the alleged chemical weapons attack site could make the UN inspectors' investigation difficult.

UN inspectors braved artillery shelling and sniper bullets to reach a town in the suburbs of Damascus that was allegedly exposed to a deadly chemical weapons attack last week.

On Monday, the 11-member team of chemical arms experts toured a field hospital in Mouaddamiyah and interviewed about 20 injured people who, six days after the purported attack on August 21, said they continued to suffer from blurred vision, shivering and lethargy.

"More than 100 people who were exposed to the chemical weapons remain in hospitals across Mouaddamiyah, but the UN investigators could not see them because they said they didn't have enough time," Adnan al Sheikh, a 31-year-old sports teacher who accompanied the inspectors, told Al Jazeera. "They were delayed by about three hours on the road from Damascus to Mouaddamiyah [a 45km trip]."

More than 355 people were reportedly killed and over 3,000 injured in the alleged chemical weapons attack on Mouaddamiyah in the eastern Ghouta region. Soon after the attack, footage emerged of lifeless bodies on the ground, and of residents shaking and foaming at the mouth at the field hospital.

The UN team collected blood samples and clothing parts from the wounded, as well as soil samples from the ground near where the rockets allegedly hit.

Obstacles to investigation

Both US Secretary of State John Kerry and UK Foreign Secretary William Hague warned that evidence could have been tampered with, degraded or destroyed in the six days since the attack. Washington and London blamed the Syrian government for not giving access to UN investigators promptly after the killings.

As the rockets travelled, we could hear a strong whistling sound that we had never heard before. Qusai Zakariya, Mouaddamiyyah resident

Syrian Foreign Minister Walid al-Mouallem, however, on Tuesday said his government reacted in a timely fashion to the request for the UN to enter the sites of the reported chemical weapons use.

In any case, experts say that it would not be too late to detect the presence of Sarin - the nerve agent Syria's opposition claims was used by President Bashar al-Assad's forces - despite the fact that this odourless and colourless liquid, much like water, evaporates quickly when released.

Juan Pascal Zanders, founder of  the-trench.org, a website that focuses on the future of disarmament and on chemical and biological weapons, said that while traces of Sarin itself would disappear only hours after being released in the air, it is possible to detect the chemical byproducts of the nerve agent.

"Chemical products, especially in blood samples, can be detected in highly specialised laboratories, even if they are days and even weeks old," Zanders told Al Jazeera.

Whistling rockets

According to residents who spoke to the UN team, the investigators also collected some parts from the rockets. Five of the alleged 29 chemical rockets fell in Mouaddamiyyah, activists said.

Residents reported that these rockets differed from the rockets and artillery shells that were usually used by Assad's forces in their daily barrage to regain this rebel-held area.

"As the rockets travelled, we could hear a strong whistling sound that we had never heard before. And when they fell on the ground, they did not fragment the way rockets usually do," said Qusai Zakariya, a 27-year-old translator who was also with the investigators.

"There were also holes in the rocket shells and the inspectors saw that. So taking samples from the rockets should hopefully help.” 

A Syrian chemical weapons scientist who had previously worked for the country’s chemical weapons programme said the rockets did not splinter because the regime adopted an "aerosol system", where rockets vent out the chemical agent as they travel, as opposed to releasing the chemicals upon explosion. The whistling sound the residents heard was the sound of the air being released, he said.

The scientist, who spoke to Al Jazeera on condition of anonymity, said it is possible to determine what chemical agents were used in these rockets even days after the attack, by examining the surface of a rocket part in specialised laboratories. 

Who is responsible?

"There are many indications that something very serious happened on August 21, that toxic chemicals were released," Zanders told Al Jazeera. The UN is tasked to find the nature of chemicals used, he said.

The UN mission, however, does not have the mandate to determine which side was responsible.

Rebels and the regime trade blame for the alleged chemical attack. The West accuses Assad’s forces of carrying it out, citing its capability and its determination to regain control of the areas around the capital.

Some opposition activists have claimed that the rockets were fired from launchers located at the Brigade 115 military base north of Damascus. Others said they believed the rockets were launched from a military base in the Qalamoun mountains.

"What makes it hard to determine where the rockets were fired from is the fact that we were being showered by ordinary artillery rockets at the same time," Sheikh said.

The Syrian scientist Al Jazeera spoke with suggested the possible use of satellite signals and images as a way to locate the launching site of the rockets. As an example, he said that in December 2012, the US army was able to confirm the launch of four short-range Scud missiles from Damascus by intercepting satellite signals.

But using this method depends on the possibility of a satellite passing over the area during that specific period, Susan Wolfinbarger, a senior researcher at the American Association for the Advancement of Science (AAAS), said. It also depends on the impact the rockets had on the ground. Previously, the AAAS had been able to trace the origin of the shells that fell during the conflict in Sri Lanka, by measuring the angle of the impact that was clearly visible in satellite imagery.

This may not be as easy in the case of the latest attack. The continuous shelling on the suburbs of Damascus by Syrian regime forces during and after the alleged chemical attack makes it difficult to identify the craters created by the rockets in question.

"The decision as to who carried out the attack will be a political one. The UN will present the facts and their findings, which will then be debated in the UN Security Council and decided upon," Zander speculated.

The UN inspectors are expected to take two weeks to investigate the incident, and have requested access to three other sites.

"The inspectors tried to take whatever they could from Mouaddamiyyah. They even took samples from animals. And despite the fact that the conditions were unfavourable, they were so determined to get to Mouaddamiyyah. I was really impressed," Zakaria said.

"A rocket fired at Mouaddamiyyah from the Fourth Brigade military base at 4pm alerted the inspectors that it was time to leave. And when they left, the town was back to being showered by rockets again.”