The issue

Russia, Syria, and the U.S. disagree about whether Syria used chemical weapons against its citizens in an April 4 attack. Russia and Syria claim Syria doesn't have chemical weapons, but the U.S. says it has evidence the Syrian government deployed the chemical attack and that Russia knew about it beforehand.

As the international community probes into who was behind the attack, here's what you need to know about chemical weapons:

The facts

A chemical weapon is commonly thought to be a commercial chemical that is used against people to cause mass casualties. But it's not just the chemical used in an attack — it's also the method of deployment, per the Chemical Weapons Convention (CWC). That means if a country possesses the munitions or equipment to deploy chemicals, but not the chemicals themselves, it is still in violation of humanitarian and criminal laws.

History: Chemical weapons were first used widely in World War I. Italian Prime Minister Benito Mussolini, Japanese Emperor Hirohito, Egyptian President Gamal Abdel Nasser, and Iraqi President Saddam Hussein have all been responsible for deploying chemical weapons.

Countries with declared chemical weapons production facilities, per the OPCW: Russia, Syria, Iran, China, Iraq, Libya, UK, U.S., France, India, Japan, Serbia, Bosnia and Herzegovina, each at various stages in destruction plans.

Syria's accountability: Although Syria is party to the Geneva Gas Protocol, it is not party to the CWC. And because Syria isn't party to the Statute of the International Criminal Court, the court prosecutor can only take up the matter if there is a Security Council resolution authorizing it.

Why it matters

The bottom line is using chemical weapons is a war crime, but no one wants to be tagged with this atrocity.