The explosion claimed the lives of Syrian Armed Forces soldiers who are apparently loyal to Assad, and the Syrian government was quick to demand an international investigation of the incident. These two facts would indicate that Assad's forces were not behind the attack.
In addition, from what has been released of the physical and medical evidence, it seems that some of the injuries were caused by chlorine. While chlorine gas has been used in the past as a weapon, mainly in the First World War, the chemical arsenals of nations developing these weapons have for decades focused mainly on mustard gas and various types of nerve agents, which, had they been used last week, would have caused different symptoms that were not observed.
It appears that the target of the attack was a checkpoint manned by Syrian Armed Forces, which reinforces the theory that rebel forces, probably jihadists known to be operating around Aleppo, were behind it. A report by Britain's Channel Four, based on Syrian military sources, claims that the weapon used in the attack may have been a missile carrying a warhead filled with chlorine mixed into a saline solution. The Syrian source also said that a factory that manufactures chlorine is located nearby.
If these claims are true, it would seem to prove that the jihadists have the technical expertise necessary to insert chlorine gas into a warhead and seal it so that the gas does not leak during launch but only upon impact with the target.
It now appears that the weapon was an improvised chemical munition, of the type used by the opposition on several occasions in the "Sunni Triangle" area during the U.S. occupation of Iraq. Whatever that thing was, it certainly wasn't a Scud-C tipped with a Sarin gas warhead.
Contrary to initial speculation, this wasn't any sort of organized military operation by the Syrian military. If it was, hundreds or thousands of people would have died almost instantly in a big area around a large crater near some militarily significant target.
Here are several sources on the 2007 Chlorine bombings in Iraq. Note that Fallujah and Ramadi are strongholds within the "Sunni Triangle" where these attacks initially took place. If the details about Chlorine-based improvised chemical weapons are accurate, this attack in Syria may be by some of the same people:
Chlorine bombings in Iraq - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Chlorine_bombings_in_Iraq Chlorine bombings in Iraq began as early as October 2006, when insurgents in Al ... February 19, 2007: A suicide bombing in Ramadi involving chlorine killed ...
Chlorine Blasts Kill 8; 6 Troops Also Die in Iraq
http://www.washingtonpost.com › World › Middle East › Iraq
Sunday, March 18, 2007 ... The chlorine bombs -- two near Fallujah and one near Ramadi -- left at least 350 people and seven U.S. soldiers ill from exposure to ...
Chlorine bombs pose new terror risk - USATODAY.com
Apr 23, 2007 – Updated 4/24/2007 8:51 AM | Comment | Recommend, E-mail | Print ... At least five chlorine truck bombs have exploded in Iraq in recent ...
Iraq Insurgents Turn to Chlorine Bombs : NPR
http://www.npr.org › News › World › Iraq
Feb 22, 2007 – At least five people died in such an attack Wednesday, the third in a ... Iraq Insurgents Turn to Chlorine Bombs ... February 22, 2007
Most likely, this event was an attempt by the Syrian opposition or its foreign backers to create some sort of Tonkin Gulf-type incident during Obama's ME trip, manipulated and telegraphed by opportunistic western intelligence and media. The other possibility is an unauthorized strike using a small quantity of some chemical stocks after someone, on one side or the other, got into an unsecured arms depot.
If you want to know who's been stoking the drive toward greater western intervention, look at the sources that continue to label this as an official Syrian military action and raise it as a "red line" violation. See, http://www.cbsnews.com/8301-3460_162-57576009/red-line-has-been-crossed-in-syria-rogers-says/ That, we know from the basic facts now emerging from Syria, is obviously not any more accurate than the lies told to get the U.S. to invade Iraq a decade ago.