Turkish media on Tuesday ran a "selfie video" of a man they say is the gunman who killed 39 people, most of them foreigners, at an Istanbul nightclub.
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The video broadcast on Turkish television shows the alleged gunman filming himself with a cellphone at Istanbul's Taksim square. It wasn't immediately clear if it was filmed before or after the New Year's massacre at the Reina nightclub.
The assailant, armed with a long-barreled weapon, killed a policeman and a civilian in the early hours of 2017 outside the Reina club before entering and firing at some of the estimated 600 people inside.
Media outlets quoted security experts as saying that the assailant, who is still at large, is a highly professional assassin.
"The assailant has experience in combat for sure ... he could have been fighting in Syria for years," one security source told Reuters, saying that he was likely to have been directed in his actions by the jihadist group.
The English-language Daily News quoted anti-terror expert Abdullah Agar as saying the way the attacker operated shows that "he is absolutely a killer and he probably shot at humans before."
Agar is quoted as saying that "the attacker is determined, faithful, practical, coldblooded expert and knows how to get results ... he probably fired bullets in real clash zones."
No details have been released as to why the authorities might think the man on the video is a suspect in New Year's attack, or how the footage was obtained.
The Islamic State group claimed the attack on Monday, saying a "soldier of the caliphate" had carried out the mass shooting in response to Turkish military operations against ISIS in northern Syria.
Turkey's state-run news agency says police detained two foreign nationals at Istanbul's main airport on suspicion of links to the deadly attack. This brings the number of suspects held in connection with the massacre to 16.
The Hurriyet newspaper said a woman identified by Turkish media as the wife of the massacre suspect has told police she did not know her husband was a member of the Islamic State.
The woman was detained in the central town of Konya as part of the investigation. Neither she nor her husband has been identified by name. Hurriyet said on its online edition Tuesday that the woman said she learned about the attack on television and told police she didn't know her husband harbored "sympathies toward" ISIS.
Media reports say the gunman flew to Istanbul from Kyrgyzstan with his wife and children on November 20. From there they drove to the Turkish capital, Ankara, before arriving in Konya on November 22.
The family rented a studio in Konya, paying three months of rent upfront. The gunman told the estate agent he had arrived in Konya in search of work, according to the report.
Hurriyet said the gunman returned to Istanbul on December 29.
There were conflicting reports over the gunman's identity.
Several media outlets on Monday, citing unnamed security sources, said the man was believed to be from a Central Asian nation and may have been part of the same cell that staged a June attack on Istanbul's Ataturk Airport that killed 45 people.
Haber Turk newspaper on Tuesday said the man is thought to be a member of China's Muslim Uighur minority. Without citing a source, the newspaper said he had arrived in Konya with his wife and two children in order not to raise suspicions.
On Tuesday, Turkish tourism industry professionals marched to the Reina nightclub, which is frequented by famous locals, including singers, actors and athletes, in a show of solidarity and to protest a spate of attacks that has crippled the sector.
About 200 people, including restaurateurs, hotel owners and gastronomy students, took part in the protest, marching behind a large banner that read: "We won't be daunted! For our tomorrows."
Turkey's crucial tourism industry has suffered enormously after a series of recent attacks in the country. The mass shooting follows more than 30 violent acts that have rocked NATO member Turkey in 2016.
Turkey launched an offensive to northern Syria in August in a bid to clear a strategic border area of ISIS militants and contain the gains of Kurdish fighters. Turkish jets are regularly bombing Islamic State targets in the Syrian town of al-Bab as Turkish-backed Syrian opposition force try to capture it from the extremists.
Also on Tuesday, the United Arab Emirates warned its citizens not to travel to Turkey following the attack, with its Foreign Ministry issuing a terse statement in Arabic to "postpone plans to travel to Turkey until further notice."
Seven of the nightclub victims were from Saudi Arabia; three each were from Lebanon and Iraq; two each were from Tunisia, India, Morocco and Jordan. Kuwait, Canada, Israel, Syria and Russia each lost one citizen.