On Monday evening, Andrey Karlov, Russia's ambassador to Turkey, was shot dead by a 22-year-old police officer in an Ankara art gallery. The shooter, who shouted "Don't forget Aleppo, don't forget Syria" after gunning down the envoy, was killed by law enforcement. At least two people who attended the event were treated for injuries.

In the wake of the Karlov assassination, Turkish leaders reached out to their Russian counterparts to offer their condolences and reiterate their commitment to cooperation with Moscow. After briefing Russian President Vladimir Putin over the phone, Turkish president Recep Tayyip Erdoğan made a statement about the incident – which he called "an act of provocation intended to disrupt the multi-dimensional cooperation between Turkey and Russia" – and noted that neither Moscow nor Ankara would fall for it. Prime Minister Binali Yıldırım spoke with his Russian counterpart to condemn the fatal attack and argued that the gunman didn't just target Turkey-Russia ties but also joint efforts to address regional problems. The two countries decided to launch a joint investigation to shed light on the envoy's assassination.

As a country that has lost many diplomats to terrorism over the years, Turkey understands the sense of loss and fury Russia and its people must be feeling today. Not only Turkish officials, but also the entire nation is mourning the murder of the envoy of Russia. With a formal investigation already underway, there are red flags all over the shocking event. First, the timing is curious: The gunman, who supposedly wanted to avenge Aleppo, took no action during the four-month bombardment in the Syrian city. Instead, he gunned down the Russian ambassador just hours before the foreign ministers of Turkey, Iran and Russia were due to meet in Moscow to resolve the humanitarian crisis in Aleppo. Then comes the footage of the shooting – where some things are off. In a clear attempt to portray himself as a member of a radical group, the assassin clumsily recited Arabic phrases a normal extremist would have recited thousands of times. No one who heard his sentences can doubt that here we have someone trying to confuse the authorities.

Finally, here are some facts we already know about the shooter. According to a senior official, he requested two days of personal leave on the July 15 coup attempt and boarded an Ankara-bound flight from Diyarbakir just minutes before the public learned about the putsch. "He arrived at Ankara Esenboga Airport just after 11 p.m., which makes us wonder if he knew about the coup attempt in advance," the official said. "What's more interesting is that several of his classmates said the shooter was sympathetic toward Fetullah Gülen, the fugitive leader of the Gülenist Terror Group (FETÖ) and two police officers who wrote recommendations for him when he applied for the police academy have been discharged since the coup attempt over Gülen links. The same goes for the police chief who approved the shooter's two-day leave request on July 15." Just three days before the assassination, senior Gülenist Abdullah Bozkurt had 'randomly' claimed that "embassies are no longer safe in Turkey." The fact that most of his friends and acquaintances had no idea that he had strong links to FETÖ is proof that he was a member, as hiding their true nature from those closest to them is their most evident trait. Again, a joint investigation will be launched to find out who the shooter really was.

While we mourn the death of Ambassador Karlov, his murder has shown the necessity of Turkey and Russia cooperating more closely on regional issues and terrorism. Yesterday's foreign minister-level meeting in Moscow marks a first step toward the peaceful resolution of the Syrian crisis and the upcoming Astana summit. Over the past six years, Turkey's allies in Washington and Brussels have proved completely unreliable if not hostile to Turkish interests on the ground. Paying lip service to removing Bashar al-Assad from power, they partnered with terrorist groups, including the YPG, and perpetuated the civil war under the pretext of fighting Daesh – in slow motion. Moving forward, Turkey and Russia need to work together to broker a deal in Syria, break the power of the terror groups and put the region back on track.

This latest tragedy shows that the measures taken by the Turkish government against FETÖ have not been effective enough to root out all the danger posed by the group. More effective and harsher strategies are called for to root out all FETÖ presence within the police and judiciary. No one should forget that FETÖ operatives still in hiding will try new tactics to harm the country.

Conducting attacks that lead to an operative's death, practically suicide attacks, is something the group had never attempted before Monday. The group's operatives had resorted to committing suicide after July 15 to hide what they know from authorities, but Monday was the first time the group conducted a suicide attack. FETÖ, through its local imam's directives, can change their tactics at a moment's notice. Recently, Fetullah Gülen himself told his followers that sacrificing oneself for the group was permissible.

Meanwhile, the Russian leadership should cooperate more closely with Turkey to address the threat posed by Gülen, who continues to operate freely out of his mansion in the United States. Especially in Central Asia, where Moscow has considerable influence, it is important for the Russians to support the ongoing effort by Turkey to hinder the group's recruitment efforts and financial operations.

The actions of Turkish and Russian leaders will determine what Ambassador Karlov's legacy will be. If we can mourn him together and hold those responsible for his untimely death accountable, Moscow and Ankara can take their partnership to the next level.