Erdogan's deputies already blamed Syrian intelligence operatives for car bomb explosions last month that killed at least 43 people, resulting in the detention of nine Turkish nationals believed to have been Syrian intelligence assets. A bombing in a Turkish border town is one thing, but the sophistication required for a subversion operation is another. Syrian intelligence tactics tend towards the thuggish and obvious -- showing up at mosques to beat people, for example. One might argue that this lack of finesse reflects the omnipotence of the head of state to whom Syrian intelligence operatives report. I'd assess the likelihood of their involvement in Turkey's latest flashpoints to be low.
Russia would like nothing more than a return to stability in Syria so it can restore normal military and trade alliances. And there's no question that Russian foreign agents are as brilliantly adept (linguistically, culturally and otherwise) at operating within Turkey, since they can feasibly be left in place for up to a decade-long rotation, as they are in classic subversion methods and tactics. But with one ally, Syria, already destabilized, and with refugees flooding into Turkey, would Russia really now want to further destabilize yet another regional trading partner? It would be like chopping off your arm to fix a broken finger.
That leaves Iran. There isn't enough space in this column to detail the laundry list of disruptive Iranian espionage activities in Syria. Couple this with the cultural and linguistic ease of Iranian agents, and Iran's penchant for black ops and proxies, and I think we have a prime suspect.
Iran's Ministry of Intelligence and Security (MOIS) has been trained by Russia's foreign spy agency. According to a Pentagon report, "MOIS infiltrates Iranian communities outside of Iran using a variety of methods. For instance, a society called 'Supporting Iranian Refugees' in Paris is used to recruit Iranian asylum seekers to spy on Iranians in France. ... MOIS's tactics of penetrating and sowing discord within the opposition abroad are discussed in an article on a Web site affiliated with the current Iranian government." The December 2012 report lists Turkey as a primary MOIS target country.
Or I suppose one could still conclude that this is all just about preserving a patch of grass in Istanbul.