The second theory is that it was the Syrian rebels. They certainly have the motive to use the weapons, blame Assad, and force the US to join on their side of the civil war. Like the Syrian government, the rebels have done some atrocious things in this fight as seen in the video of a rebel commander who cut out a dead Syrian soldier's heart and ate it. A large amount of the rebel opposition are Islamic extremist groups who oppose Syria's secular regime. The Syrian branch of the Muslim Brotherhood and the Al-Qaeda-linked Jabhat al-Nusra are two of these with the later openly demanding that Syria become an Islamic state under Sharia law. It's hard to imagine wanting these groups to take over power in Syria either.
Dale Gavlak, an independent journalist who has done work for Associated Press, has reported that rebels have said they had gotten the sarin gas from Saudi Arabia and then mishandled it, causing the accident. Saudi Arabia has made its desire to overthrow the Assad regime clear in the past. Neither Russia or Syria have provided any evidence that the rebels were responsible.
A third theory was put forward by retired US Army Colonel Lawrence Wilkerson, the former chief of staff to Colin Powell during the Bush administration. He said the evidence that Assad used the chemical weapons was "flaky" and that it could have been the rebels or even Israel who used it in order to draw in the US. Certainly, Israel supports removing Assad due to his close relation with Iran and his material support of Hezbollah who were able to fight Israel out of Southern Lebanon in 2006. This is just idle speculation but something worth thinking about if only because there is an actual motive.
As to who it actually was, I'm having as much trouble figuring this out as everyone else it seems. Assad has said his regime is innocent. Obama and US Secretary of State John Kerry certainly believes it was him. White House Chief of Staff Denis McDonough says a "common-sense test" dictates that it was him although also says they don't have "irrefutable, beyond-a-reasonable-doubt evidence." As of yet, however, it seems all of the evidence is circumstantial or classified.
The US says they possess satellite imagery showing attack preparations and transcripts of Syrian forces detailing the attack plans but refuse to disclose any of them. Essentially all the the US is saying is that the attack was too big and coordinated to be the rebels. Even the actual estimate that Obama put forward of 1429 deaths in the attack is controversial. The Western-supported Syrian National Coalition was only able to provide a list of 395 deaths, many of them only mentioned by first name or as relative to another name.
Honestly, it's hard to imagine that the US has any evidence at all. Leading up to the Iraq War, evidence was at least created fraudulently and presented to get UN support. Now though, people are a little more wary of the country who cried WMD. The evidence would be closely examined so it seems safer for the Obama administration to simply say it has it rather than faking it. Obviously, any real evidence would have been presented already.
Now the second question, is limited missile strikes on Syrian forces an effective and logical response? Well, both the rebels and Syrian President Bashar al-Assad have agreed that the missile strikes would do nothing. There might be a few civilian casualties and possibly a couple military personal dead but nothing would change. It's already been made clear that the weapons can't target chemical weapons sites since that would possibly release them. Not even mentioning that Tomahawk cruise missiles aren't free and thus should probably be used wisely.
Although Obama pushed heavily for military intervention in Syria immediately following the gas attack, a majority of American people are against any attack of Syria even if it turns out Assad was responsible. Obama, the constitutional scholar, was kind enough to remember the Constitution's separation of power and turn a vote to go to war over to Congress who is supposed to hold that authority. Considering the lack of support for attacking amongst the US public, it seems unlikely that Congress will go along with it, what with their entire House of Representatives and a third of their Senate up for reelection in 2014.
Really, few supporters of attacking can be found outside of the country either.
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