Why Iran? Surely Russia is a bigger suspect, but right now, my biggest suspect would be the NSA/CIA, the timing of the Syrian escalation is just too perfect.
In the middle east Iran* probably has the greatest geopolitical reach of any country within the region. Through Hezbollah they have an enormous impact on Syria, Lebanon, the Palestinian territories and even Israel. If the al-Assad regime falls Iran has the most to lose as suddenly it would become far more difficult, logistically and otherwise, to provide support to its groups in the Levant.
This explains why Iran is threatening action if the US bombs Syria, for example.
The Putin regime has certainly shown itself capable of significant international "hijinx" (such as assassination, vote rigging, etc.) but overall this doesn't fit their MO.
(*: note that when I say "Iran" here I am talking about the current Iranian regime, very much not the Iranian people.)
Dusting off my tin foil hat, I would go with Israel in collusion with the NSA/CIA. They have the most to gain by turning the media against Syria and the technical capabilities as proven with their involvement in stuxnet.
http://en.wikipedia.org/wiki/Stuxnet
You think that Israel wants a war with Syria? Syria could easily turn those chemical weapons across its border. I think Isreal is probably one of the big factors causing US restraint right now.
But my tin-foil hat hasn't been working very well lately so the government radio signals may be blocking me from seeing something.
Things are enough of a powder-key economically this sort of thing to get out-of-hand in a big way.
China and America are co-dependent but at cyber-cold-war. Russia just recently gave the middle-finger to the U.S. with Snowden and we refused to meet with each other. The two primary powers that emerged after the last world war are no longer at the top so there is an open gap for who's next: the U.S. who no one wanted to mess with is overstretched, underfunded, and there is no better president to have at the helm if you want a war with the U.S. than one who has not achieved much militarily other than social reform and withdrawal, is on the edge of economic shambles due to decades of overspending much more than the stock market and media would lead you to believe, and whose party's voting constituents aren't in favor of a war, and Russia, who turned into a mafia-run state with former KGB at the helm that are unable to elicit much nationalism- much less a military power it used to be, doing the equivalent of selling its military assets on ebay for years.
Mass executions from chemical attack or otherwise are not the reason we are getting involved. This is a power struggle. Some big players (Clinton comes to mind) in U.S. Democratic party are set on cleaning up the Iran/Syria/Lebanon area, and Republicans are always up for a war. But, I'm afraid they will get more than they bargained for.
Why is Russia a bigger suspect? A study of foreign policy and defence would appear to suggest that Iran perceives that it is under threat of invasion from America.
If I seriously believed I was under actual threat of invasion from the US, I am not sure I would piss away my resources getting monkeys to deface a brochure.
Why do you suspect this is sanctioned by Russia? What would they have to gain from pestering a couple media companies, especially at the risk of losing their business? What is your logic here?
