Last week, the White House announced that they had evidence of chemical weapons use inside of Syria, which reaffirmed reports from Britain, France, and Israel [link]

However, the President did not offer very much in the way of details. "We don't know how they were used, when they were used, or who used them," President Obama said to the press.

The lack of clarity — and certainty for that matter — is unsettling. The White House and other global leaders worry that "a red line" has been crossed in Syria, and that chemical weapons might soon fall into the hands of terrorist organizations in the region, like Hezzbollah. And over the weekend, Israel bombed a suspected military research center and a weapons convoy traveling from Syria to Lebanon.

Meanwhile, our knowledge over Syrian use of chemical warfare currently amounts to mostly speculation.

The majority of reports to this point suspect that sarin, a nerve gas that shuts down the respiratory system, was the chemical agent used in March near the city of Aleppo, when these allegations first surfaced. When weaponized into a liquid spray (aerosol), sarin can be inhaled or absorbed through the skin and eyes within minutes.

"Some of the symptoms we see [on videos of the Aleppo attack] are consistent with exposure to a nerve agent like sarin," said biological warfare specialist Gregory Koblenz to the VOA. But "just the videos alone don't provide enough information and context to really assess what happened to these people."

United Nations human rights investigotors have also obtained first-person testimony supporting these suspicions. However, the investigators say their report cannot serve as "conclusive findings".

Blood samples from the victims of the Aleppo attack were positive for sarin poisoning, according to WIRED, but many are disputing the provenance of the specimens. Last week, the Guardian reported that new questions have emerged "amid apparent inconsistencies between eyewitness accounts describing one of the attacks and textbook descriptions of the weapon." Moreover, there are claims that not all of the sarin-positive samples originated from Aleppo.

The United Nations wants to conduct its own investigation of soil and blood, but requires access to the targeted regions. This access is being denied by the Syrian regime. And the clock is ticking.

Once sarin hits the bloodstream, the toxin destroys an enzyme — acetylcholinesterase — that works as an off-switch for muscle contractions. Without this off-switch, muscles in the lungs eventually fatigue to the point of failure, and a person suffocates.

There is a time limit for when scientists can detect fluctuations in acetylcholinesterase. Blood levels of this enzyme can in some cases serve as an indication of poisoning, but if many days have passed, the samples from survivors could be inconclusive, said chemical weapons expert Dr. Christopher P. Holstege, Chief of Medical Toxicology at the University of Virginia School of Medicine.

On the other hand, inspectors have a few additional days to detect byproducts produced when the body breaks down the chemical agent - 'sarin metabolites', as was the case for the clinical investigation of 1995 sarin attack of the Tokyo subway system.

"For example, in the Tokyo subway attack, reports documented that the sarin metabolites were detectable in the urine up to one week after exposure," said Holstege, but a high level of exposure is needed to expand the window of detection.

Dr. Holstege has assisted law enforcement with clinical investigations into poisonings and written a book along with several papers on the topic. He told Medical Daily that in an investigation like this, there is often a 3-pronged team of professionals who assess the allegations:

1. Clinical toxicologists will collect medical records and interview patients on their symptoms.

2. Analytical toxicologists will test human samples for the presence of the weapon.

3. A third group of scientists would "collect and subsequently submit environmental samples for testing, such as soil, exposed clothes, etc."

The shelf-life for sarin in environmental samples varies 3 from weeks to months — depending on the purity of the weaponized mixture, which is why the UN chief is urging the Syrian government to allow its investigators into the country.

"As we address these allegations," said Secretary-General Ban Ki-moon, "I encourage all involved to uphold their responsibilities in enabling us to properly police these heinous weapons of massive destruction," according to the AP.