Ambassador's Death Complicates Russian, Turkish Cooperation in Syria

— -- The brutal assassination of the Russian ambassador to Turkey during a televised event at the Museum of Modern Art in Ankara on Monday left observers shocked and appalled, but also asking difficult questions about the relationship between Turkey and Russia.

The shooter has been identified by local police as Mevlut Mert Aydintas, 22, a member of Ankara’s riot police. Aydintas stood over the slain ambassador's body, shouting in Turkish to terrified onlookers: "Don't forget Aleppo, don't Forget Syria," and "God is greatest."

Shortly after he was gunned down by security forces.

It is not yet clear if Aydintas was connected to any known terror groups or if he was motivated or working as part of a wider plot. Local police say they are still investigating many leads and have taken into custody at least seven people for questioning, including members of Aydintas’ family and his roommate.

Nevertheless, the shooter's own words explain at least some part of his apparent motivation: the war in Syria.

Syrian War

In the lead-up to this attack, Russian and Turkish relations have been on the mend despite the fact that they have opposing interests in the war. The Russian government has backed the Syrian regime with military support since the summer of 2015 and Turkey has in large part aligned itself, religiously and politically, with the interest of the rebel forces battling Syrian President Bashar al-Assad for control.

Relations fell to a dangerously low point in November of 2015 when Turkish F-16 fighter jets shot a Russian warplane out of the sky after repeated violations of Turkish airspace, sparking fears of war. As a NATO member, any provocation against Turkey would call for ally members, including the United States, to defend it.

But Russia never responded and chose instead to keep up its relentless bombing campaign inside Syria. As Russia steadily turned the tide of the war back into Assad's favor, Turkey became embroiled in its own internal crisis. Following a failed military coup this summer, which left hundreds dead, Turkish President Recep Erdogan has arrested tens of thousands of Turkish citizens in a so-called "purge" of enemy forces, including journalists, educators and members of the military. Accusations of torture have led to an international outcry.

"There was a considerable recalibration of Turkey's approach to Syria over the summer where the emphasis shifted from forcing Bashar al-Assad from power...and they began to focus almost exclusively on preventing Kurdish expansionism inside of Syria," Aaron Stein, a Middle East expert at the Atlantic Council in Washington, told ABC News.

The Turks have been in a years-long conflict along their southern border with a group of Kurdish fighters the U.S. has strongly supported in the Syrian civil war. The reluctance by U.S. officials to waiver on that support, even in the wake of terror attacks perpetrated by that group inside Turkey, "left Turkey upset with U.S. policy inside Syria," Stein said.

But Erdogan found a scapegoat for both the coup and the war: the United States.

The United States

The souring of relations between the U.S. and Turkey during the Syrian war helped pave the way for Turkey's warming relations with Russia. "Russia doesn't have to do much to play off those issues," Stein said.

Erdogan blamed the failed coup on the movement of Fethullah Gulen, a exiled cleric living in Pennsylvania. The Gulen movement is designated as a terrorist organization by the Turkish government, which has equated the group’s leader to Osama bin Laden. Turkish leaders said Washington's failure to immediately extradite Gulen had "negative" effects on their relationship.

Turkish officials have even accused the assassin in Ankara as being a member of the Gulenist movement.

After the U.S. and Russia failed on multiple diplomatic efforts to reach a cease-fire deal inside Syria, Turkey and Russia took the lead. Representatives from Turkey, Russia and Iran met in Moscow today to discuss the future of Syria and the besieged city of Aleppo, notably without the participation of the United States.

But because the U.S. has such a vested interest in the war, observers like Stein believe Russia and the Turks are waiting to negotiate with the incoming Donald Trump administration, which has signaled it will be more supportive of Russian objectives in Syria.

What's Next?

In televised remarks yesterday, Russian President Vladimir Putin said the ambassador’s murder was "undoubtedly a provocation aimed at disrupting the normalization" of bilateral ties and the "peace process in Syria."

Erdogan made similar claims, saying, "We know that this provocation is aimed at damaging improving Turkish-Russian relations."

But in a gesture of solidarity, Turkey’s foreign minister announced Monday that the street where the Russian embassy is located will be re-named after the slain ambassador, Andrey Karlov.

Putin has promised retaliation, but it is unclear where that will be directed other than to embolden his relentless support for Assad.

"If anything, Russia has the incredible incentive to play to Turkey's tune here," Stein said of the assassination, "because they're blaming Fethullah Gulen again and this will cause problems with the U.S., Turkey relationship."

ABC News' Patrick Reevell and Marcus Wilford contributed to this report.