Immediately after the shoot-down of a Russian bomber jet near the Turkish-Syrian border, Ankara and Moscow told two different stories. Turkey claimed:
  • it warned the Russian jets 10 times in 5 minutes (presumable before airspace violation) to change their course
  • the Russian jets violated Turkish airspace for 17 seconds ("to a depth of 1.36 miles and 1.15 miles in length)
  • the downed jet was fired upon by Turkish F-16s "while in Turkish airspace"
In contrast, Russia claimed:
  • no warnings were received
  • the jets did not violate Turkish airspace; the downed jet was shot down 4 km from Turkish border
  • a Turkish jet entered Syrian airspace to target Russian jet
Both sides have released maps showing the alleged violation (or not). Here they are roughly overlaid, showing that the alleged flightpaths do not correspond. The Turkish one clearly shows the Russian jet crossing over Turkish territory (dotted pink) 1-2 km from the southern border; the Russian one shows it avoiding the border (solid red) by around 1 km.
turkey map

The Russian map shows the Turkish jet briefly entering Syrian airspace.
The Syrians concur, their foreign minister calling it an aggressive violation of Syria's sovereignty and proof of Turkish support for terrorism:
"We express our condolences over the actions of those terrorists, who Erdogan and his government support, who opened fire at the pilot as he was parachuting down. It was no less than a war crime," he said. "We are glad that the joint Russian-Syrian military operation resulted in a rescue of the second pilot," he added.

Naryshkin said the attack on the Russian plane did not reflect what the Turkish people want from its leadership. "We believe this act was treason by the Turkish leaders against their own people," he said.

Turkey deliberately attacked the Russian warplane in revenge for the Russian antiterrorist campaign in Syria, according to the Syrian minister. "The effort to destroy the forces of Islamic State [IS, formerly ISIS/ISIL] and other terrorist groups offended Turkey. That is why they aggressively violated Syria's sovereignty and attacked the Su-24 in its airspace," Muallem said.
Can't argue with him there.

As for Turkey's claim that it "repeatedly" warned the Russian pilots, the jet's navigator, who survived the crash and was rescued by Syrian forces, is adamant that they received no such warnings:
"It's impossible that we violated their airspace even for a second. We were flying at an altitude of 6,000 meters in completely clear weather, and I had total control of our flight path throughout. ... In actual fact there were no warnings at all. Neither through the radio, nor visually, so we did not at any point adjust our course. You need to understand the difference in speed between a tactical bomber like a Su-24, and that of the F16. If they wanted to warn us, they could have sat on our wing. As it was, the missile hit the back of our plane out of nowhere. We didn't even have time to make an evasive maneuver."

As the plane was hit and went down in Syria, the two pilots ejected. Captain Sergey Rumyantsev was killed, with a rebel Turkmen brigade claiming they shot him to death while he was still parachuting. Murakhtin was extracted in a 12-hour joint operation by Russian and Syrian special forces, in which a Russian Marine died.

The 39-year-old airman, who won the Top Navigator award at Russia's biggest military flying competition last year, says he will ask to return to front-line service as soon as he is declared fit. "I must 'pay back' the debt for my captain," said Murakhtin.
But for the sake of argument, assume the Turkish account is true. The area where Turkey says its airspace was violated is only 2-2.5 km wide. At max speed (1600 km/h; 0.44 km/s), the Su-24s would cross the area in around 6 seconds. If the Russian jets really did violate Turkish airspace for 17 seconds, the jets would have been traveling at around 530 km/h.
turkey map
Essentially, the Turks shooting down this Russian jet is the equivalent of shooting one's neighbor for briskly walking over the corner of your front yard.

There was no reason for shooting down the jet: it posed no threat to Turkey. Additionally, no visual contact was made, no warning shots were fired. Instead, the attack was sudden, without warning, and the jet wasn't in Turkish airspace long enough for it to crash there: it crashed in Syrian territory. Given the tiny distance involved, and the fact that by the time the jets would've entered Turkish airspace they would have already been on their way out of said airspace, this is the equivalent of shooting your neighbor in the back as he steps off your lawn and back onto his own. Following normal protocols, Turkish jets should have escorted the Russian jets out. It would have been easy. In fact, it would've taken them less than 10 seconds.

Turkey is one to talk. They (not to mention the U.S., France, Australia, the UK, Canada, the Netherlands, and Jordan) routinely violate Syrian airspace. By their own standards, Syria is well within its rights to shoot down any foreign jets daring to enter Syrian airspace. In fact, Syria did shoot down a Turkish jet violating Syrian airspace in June 2012. Erdogan responded, "even if the plane was in their airspace for a few seconds, that is no excuse to attack. It was clear that this plane was not an aggressive plane. Still it was shot down." The Turkish General Staff said, "We would have shot down 114 planes if every aircraft that violated a country's airspace were shot down without questioning. Air space violations are incidents that happen almost every day, and are resolved in a matter of minutes within international law." Apparently not, when it comes to Turkish airspace.
turkish airspace violations
Turkey also routinely violates Greek airspace. Back in 2005 they did so an average of 40 times a day, according to Wikileaks. Last year they violated Greek airspace 2,244 times. On October 6 and 7, 2015, Turkey violated Armenian airspace: they were not shot down. I suppose the Greeks and Armenians now have a precedent for shooting down Turkish jets. Surely NATO will fully defend their "territorial integrity" if they did. (Not!)

Even if the jets did violate Turkish airspace (which I doubt), it makes little difference. (Remember this: Did Russia violate Turkish airspace? Or did Turkey just move its border?) Turkey's response was excessive and completely unacceptable. It was no defensive maneuver; it was a blatant, premeditated act of war. There were reports in October that Erdogan had been planning exactly this scenario. And besides being a treacherous and cowardly act, it reeks of hypocrisy and blatant double standards. But the Turks have their reasons.

After the G20, Putin revealed that ISIS has been getting its $millions from people in 40 nations, including some members of the G20. He didn't name names. The message should have been clear: "we know who you are, but we're willing to play nice if you change your act from now on." Most of that funding comes from the sale of illegal oil, and the day after Putin's revelation, the U.S. made a show of striking just over 100 ISIS oil tankers. Since then, Russia has taken out over 1000. You'd think that Turkey would've taken the hint. Apparently not. They obviously weren't pleased. Incidentally, the jets involved in yesterday's incident were returning to the Latakia airbase after a mission targeting the remaining IS oil convoys.

But now that Turkey showed its hand, Putin isn't holding back. During his meeting with the King of Jordan the day of the attack, Putin made clear Turkey's close relationship with ISIS, calling it a "terrorists' accomplice" and explicitly stating what everyone knows but no one says publicly:
We have long been recording the movement of a large amount of oil and petroleum products to Turkey from ISIS-occupied territories. This explains the significant funding the terrorists are receiving. Now they are stabbing us in the back by hitting our planes that are fighting terrorism. ... If ISIS is making so much money - we are talking about tens or maybe even hundreds of millions, possibly billions of dollars - in oil trade and they are supported by the armed forces of an entire state, it is clear why they are being so daring and impudent, why they are killing people in such gruesome ways, why they are committing terrorist attacks all over the world, including in the heart of Europe.
We have always treated Turkey not merely as a close neighbour, but as a friendly state. I do not know who benefits from what has happened today. We certainly do not. Moreover, instead of immediately establishing contacts with us, as far as we know Turkey turned to its NATO partners to discuss this incident. As if we had hit their plane and not the other way around.

Do they wish to make NATO serve ISIS? I know that every state has its regional interests, and we always respect those. However, we will never turn a blind eye to such crimes as the one that was committed today.
According to Russia's LifeNews, Erdowanker's own son, Bilal (Turkey's new Minister of Energy, as of yesterday), is associated with the flow of ISIS oil into his country. He's reportedly the owner of some 500 trucks used to get the oil from Syria to Turkey. Here he is posing with two alleged ISIS colleagues:

bilal erdogan
Other pictures are floating around Turkish social media claiming the same thing. Russian PM Medvedev says the Turkish middlemen include government officials: "Turkey's actions are de facto protection of Islamic State. This is no surprise, considering the information we have about direct financial interest of some Turkish officials relating to the supply of oil products refined by plants controlled by ISIS." Yeah, the Turks are probably pretty pissed off. How dare Russia bomb their head-chopper cash source!

It there was ever any doubt about where Turkey's true allegiances lay, just listen to the head of Turkey's National Intelligence Organization, Hakan Fidan:
Mr. Hakan Fidan, Turkish President's staunchest ally, condemned Russian military intervention in Syria, accusing Moscow of trying to 'smother' Syria's Islamist revolution and serious breach of United Nations law.

"ISIS is a reality and we have to accept that we cannot eradicate a well-organized and popular establishment such as the Islamic State; therefore I urge my western colleagues to revise their mindset about Islamic political currents, put aside their cynical mentalité and thwart Vladimir Putin's plans to crush Syrian Islamist revolutionaries," - Anadolu News Agency quoted Mr. Fidan as saying on Sunday.

Fidan further added that in order to deal with the vast number of foreign Jihadists craving to travel to Syria, it is imperative that ISIS must set up a consulate or at least a political office in Istanbul. He underlined that it is Turkey's firm belief to provide medical care for all injured people fleeing Russian ruthless airstrikes regardless of their political or religious affiliation.

Recently as the fierce clashes between Russian army and ISIS terrorists are raging across the war-torn Syria, countless number of ISIS injured fighters enter the Turkish territory and are being admitted in the military hospitals namely those in Hatay Province. Over the last few days, the Syrian army with the support of Russian air cover could fend off ISIS forces in strategic provinces of Homs and Hama.
There's one good thing to come out of this criminal act: it's now clear for all the world to see that Turkey is a direct supporter of ISIS and, by association, so are their NATO allies.