Let's delve into Turkey a little bit more today.
First, a little backstory for those who don't know their Russia/Turkey basics: Russia has long coveted a warm-water port on the Mediterranean. (Yes, they have Vladivostok on the Pacific, but that's not enough to be a truly global power.) For that reason, Russia has long coveted Istanbul. Syria and the Ukraine both have warm-water ports - Tartus in Syria, Sevastopol amongst others in the Ukraine. This brief article is a very good run down on the topic.
Look at a map: Turkey is right in the way of Russia's access to the Mediterranean (even a Russia that includes the Ukraine, as the USSR did). Throw a little Orthodox Christianity vs. Islam in there for flavor, and you have all the makings of one of the world's oldest and most enduring rivalries.
Now let's look at the present day. The NY Times has a good summary of the issues. In a nutshell: when the civil war began in Syria, Prime Minister (and de facto dictator) Erdogan in Turkey saw it as a good opportunity to install a friendly, pro-Turkey regime on its very border - and who can blame him? A fairly rational national security choice, even if many have to die to attain this end - and as such began aiding anti-Assad rebels, some of whom are democrats but many of whom are not very good people. (Assad is also a tremendous monster.)
Russia, however, has long stood by the Assad regime, and in order to get access to Tartus and also tweak the nipples of both Turkey and the United States, has been bombing the daylights out of the Syrian rebels, with the end result that Assad is likely to finally win the battle in Aleppo.
So, when a Turkish national shoots the Russian ambassador to Turkey calling for jihad and urging people not to forget Aleppo, it should come as no big surprise to anyone, even when the event itself is quite shocking.
Since it's become clear that Assad is likely not going anywhere in Syria, Erdogan has shifted his aims from dislodging Assad to dealing with those pesky Kurds. The War Nerd talks about the Kurds a little bit. It's a good read. (More here. The War Nerd is a must-read, always.) The Kurds are hanging tough with no country to call their own, on their own, at the mercy of the powers around them. The analogy to the Zionists in Palestine before the creation of Israel isn't perfect, but it isn't bad, either. Assad, Erdogan, and the Iranians would all rather there be no Kurds. My opinion? Support the Kurds.
Erdogan is going to quit attacking Assad and instead focus on taking care of his Kurdish problem. Meanwhile, the Russians don't want the Turks to start backing the Syrian rebels again: they want to mop up in Syria. So Russia isn't going to make a big stink over one l'il assassination, and Turkey's going to do it's best to play nice, say sorry, and move on. Russia and Turkey might even grow closer as a result of the assassination (though we'll see).
Meanwhile, who was the assassin? Was he a Gulenist? Boy. How do I succinctly describe the Gulenists? Imagine a dictatorship was using the omen of a organized conspiracy directed by one man living abroad as an excuse to round up political opponents and up the level of suppression generally, and it turned out the conspiracy in question was real honest-to-goodness conspiracy. That's more or less the situation you have with the Gulenists.
Fethullah Gülen, who lives in Pennyslvania, has long spearheaded a movement of Islamists who have attempted to infiltrate the judiciary and other state organs of Turkey and take over the country from within. Meanwhile, a completely different set of Islamists, operating publicly under Erdogan's leadership, having previously worked alongside the Gulenists to attack the common enemy - the secularists, who have a long history of committing coups themselves - have now turned against them, the Gulenists having dealt the initial blow. If you have time, just read that New Yorker article. The fact that the U.S. harbors Fethullah Gülen is a source of tension in the Turkey-U.S. relationship, as you could imagine.
Well, anyhow... I've rambled here, but I hope you have a slightly greater appreciation of what's going on between Turkey, Russia and the others than you did before. Just be aware that Turkey has a terrorism problem, NATO has a major base for Middle East operations in Turkey, Incirlik, which Turkey could in theory open to Russia, and that... God, there's so much to say.
It's all going to be very interesting to watch unfold.