Story highlights
NEW: ISIS' unusual claim of an attack in Turkey could mark "a declaration of war," analyst says
Of 39 killed, 27 were foreigners, 11 were locals, and one person remains unidentified
ISIS claimed responsibility for the New Yearâs attack at Istanbulâs Reina nightclub that left 39 people dead, but authorities are still scrambling to find the killer.
ISISâ claim, made in a statement posted to Twitter, cannot be independently verified by CNN. But it boasted about the first major terrorist attack of 2017.
âIn continuation of the blessed operations which ISIS carries out against Turkey, a soldier of the brave caliphate attacked one of the most popular nightclubs while Christians were celebrating their holiday,â the statement read.
Both Turkish and US officials have called the attack an act of terrorism.
Hereâs the latest on the investigation, the victims and why Turkey keeps getting targeted:
The investigation
Investigators have found the fingerprints of the suspect and know what he looks like, Deputy Prime Minister Numan Kurtulmus said Monday.

Eight people have been detained in connection with the attack, Kurtulmus said, but the suspect was not among them.
âWe will find him, no delay,â Turkish Prime Minister Binali Yildirim said.
Footage of the attacker showed him shooting a security guard and police officer at the entrance of the nightclub. Turkish authorities said they believe he carried out the attack alone.
Earlier Monday, the militant Kurdistan Workerâs Party, or PKK, distanced itself from the attack.
âNo Kurdish forces have anything to do with this attack,â the PKK said. âThe Kurdish freedom fight is also the fight for democratization of Turkey. Thatâs why we wonât target innocent and civilian people.â
The victims
Those killed in the attack were from 14 countries, including India, Morocco, Jordan, Canada, Russia, Tunisia, Saudi Arabia and Kuwait.
Istanbul attack victims
Security guard Fatih Cakmak was one of the first victims killed. He had considered himself lucky after surviving a December attack outside Istanbulâs Vodafone Arena, where he was also working security.
âHe went to work, and now heâs gone,â said his father, Hassan Cakmak, who said he canât believe he survived his 32-year-old son.
Lubna Ghaznawi, a young female entrepreneur from Saudi Arabia, was also killed. The 34-year-old worked full-time as a communications manager for one of Saudi Arabiaâs largest banks and also co-owned a start-up with her sister called Exclusave Card, the first student discount card in Saudi Arabia.
âShe was an optimist and loved going to new places,â her friend Seham al-Shahrani told CNN. âLaughter and happiness filled whatever place she went to.â
Dozens of people were hospitalized. As of Monday, 46 were still being treated, including one American, according to the Istanbul governorâs office. A handful of the injured were in critical condition.
âWe were having funâ
Witnesses described how the festive evening turned into a bloodbath.
âWe were having fun. At first we thought it was a fight, then there was a lot of gunfire,â witness Yunus Turk told CNN.
âAfter the gunfire everyone started to run toward the terrace. We ran as well. There was someone next to me who was shot and fell on the floor. We ran away and hid under the sofas.â
READ: International community mourns Turkey attack victims
Another witness said he didnât know how many attackers there were, but he saw one person and hid.
âI got shot in the f****** leg, man,â he told journalists as he was taken into an ambulance. âThese crazy people came in shooting everything.â
On Sunday, the club issued a statement on its Facebook page.
âThis terrible incident is a terror attack against our citizensâ peace, brotherhood, serenity, economy, tourism and against our nation,â the statement read.
âOur hearts bleed and the bullets are in our heart.â
Why Turkey keeps getting targeted
Turkeyâs deputy prime minister said he believes the attack was committed in response to Operation Euphrates Shield, Turkeyâs ground operation against ISIS in Syria.
But the country is âfighting a two-front war â against the Kurdish Workersâ Party, and against the Islamic State,â CNN intelligence and security analyst Bob Baer said.
Turkey shares a 500-mile (800-kilometer) border with Syria, making it relatively easy for ISIS fighters and supplies to cross.
âThat border is so porous â weapons, explosives, people coming across it,â Baer said.
Both ISIS and Kurdish militants have launched attacks in Turkey, which is also reeling from a bloody and failed military coup in July.
Officials suspect ISIS was responsible for the attack on Ataturk Airport in June that left 44 people dead and an explosion at an August wedding that killed at least 54 people.
ISIS has typically refrained from claiming responsibility for attacks in Turkey to create âan environment of suspicion in Turkish politics,â analyst Soner Cagaptay wrote for CNN last year.
So ISISâ claim of responsibility for Sundayâs nightclub attack could mark a turning point.
âI think with Istanbul, itâs a declaration of war on Turkey,â Baer said.
Meanwhile, Turkish security forces clash almost daily with rebel PKK militants, mostly in predominantly Kurdish parts of southeastern Turkey.
In December, a pair of bombings in Istanbul killed 44 people and wounded 155 others in an attack by a breakaway group of the PKK. The two explosions occurred after a heavily attended soccer game at Besiktas Vodafone Arena.
Also in December, a car bomb exploded near a public bus, killing 13 soldiers in the central province of Kayseri. Three days later, a gunman assassinated Russiaâs ambassador to Turkey at an Ankara art gallery.
âThe issue of a copycatâ
So how could the attack at the Reina nightclub have implications elsewhere?
Nightclub attack: Full coverage
Since the assailant used a gun, and apparently started by killing the security guard, a similar attack could happen anywhere, CNN senior law enforcement analyst Tom Fuentes said.
âYou have the issue of a copycat,â he said. âSo here in the United States, we have over 300 million guns at large in our population. So weâre talking about one person getting a hold of one of those guns and launching an attack and doing it on his own. ⦠So itâs almost impossible to stop, if thatâs what we end up with â a lone wolf who wants to get a gun.â
CNNâs James Masters, Karen Smith, Sara Sirgany, Steve Almasy, Gul Tuysuz, Nadeem Muaddi, Laura Koran, Joel Williams, Steve Brusk, Mayra Cuevas and Darran Simon contributed to this report.