What is the ISIS top chemical weapons engineer telling the US?

US special forces captured a top Islamic State engineer in February, and he has already provided information on the terrorist group's supplies and plans for chemical weapons. 

Sleiman Daoud al-Afari, who worked under Saddam Hussein as a chemical and biological weapons expert, is being questioned by American military officials in Erbil, Iraq, The New York Times' Helene Cooper and Eric Schmitt reported. 

Mr. al-Afari has told American interrogators that ISIS is weaponizing mustard gas by loading the powder into artillery shells, although officials told The Times it was likely not concentrated enough to kill. 

Mustard gas, while fairly easy to produce, is difficult to effectively weaponize, says Roby Barrett, a scholar associated with the nonpartisan Middle East Institute in Washington, D.C., in a phone interview. For a terrorist organization such as the Islamic State, the main impact of possessing chemical weapons is psychological. ISIS likely hopes to frighten Iraqi troops by threatening to employ the gas on the battlefield but does not have the logistical expertise or resources to carry out the kind of chemical attacks that terrorized the anti-Assad Syrians or the Kurds under Saddam Hussein. 

ISIS has used mustard gas in 12 confirmed cases and three suspected cases, but information from al-Afari has aided US plans to locate and destroy two weapons centers, Barbara Starr reported for CNN. The terrorists' use of such weapons has caused no casualties so far, as the group lacks "chemical capabilities," Iraqi Defense Minister Khaled al-Obaidi said, according to the Associated Press.

The threat of a chemical weapons attack has worried the public since 9/11, so although the US government has an interest in reassuring the public that it has the situation under control, the terrorist group's more practical – and potent – weapons are likely still guns and explosives, Mr. Barrett says.

"I think it’s something that has to be watched, it’s something that really grabs media attention, but it’s something that’s much more difficult for them to deploy and use," Barrett says. "It’s much more complicated than using explosives or guns."

Both the capture of the top ISIS engineer and the use of information he has provided reflect the first signs of efficacy from the US government's so-called "acceleration" since December, as The Christian Science Monitor's Anna Mulrine wrote:

The heart of the “further accelerated” version of the anti-IS campaign consists largely of more US troops, for training Iraqi forces and for conducting targeted strikes both from the air and on the ground. Soldiers from the 101st Airborne Division headquarters and the 2nd Brigade Combat Team out of Fort Campbell, Ky. – a brigade can include anywhere between 3,500 to 5,000 forces – will head back to Iraq later this year. 

This contingent also includes “special operations forces of the sort that we don’t talk about a lot, but that we’ve introduced in a number of different ways,” [Defense Secretary Ashton] Carter told reporters.

Commandos in one of these forces, called American Special Operations, according to The Times, captured al-Afari. The capture and the information the detainee provides have enhanced the US military's ability to attack stockpiles of IS weaponry, but its impact on terrorist threats outside the region is likely negligible. 

"The likelihood of a real, successful gas attack is pretty low," Barrett says.