Turkish authorities on Monday released the clearest image yet of the man believed to have wreaked havoc on a nightclub full of New Year's Eve revelers, and officials believed they were closing in on positively identifying the gunman.
ISIS on Monday claimed responsibility for the attack, which killed 39 and injured about 70, and Turkish media reports had said investigators believed the killer was likely from Uzbekistan or Kyrgyzstan. The discovery of new evidence at the scene of the attack was also bolstering the effort to name the suspect -- who remains at large.
"Information about the fingerprints and basic appearance of the terrorist have been found," Deputy Prime Minister Numan Kurtulmus said at a Monday news conference. "In the process after this, work to identify him swiftly will be carried out."
Turkish investigators detained eight people Monday in connection with the attack on the Reina nightclub, however, none were believed to be the gunman. It was unclear how the eight people may be connected to the attack, which had indications of planning, including the possibility that the gunman cased Reina before the massacre.
"He stormed in and immediately headed for the people to the left, which is always more crowded...I wonder if he came here before because he seemed to know where to go," barman Mehmet Yilan told Reuters.
Experts who had viewed full video of the attack told pro-government Turkish paper The Daily Sabah that the assailant appeared professionally trained. He reportedly fired more than 180 bullets during an episode that lasted about seven minutes before going to the kitchen, changing his clothes and escaping by blending in with the fleeing crowd.
A statement distributed by ISIS said the attack was carried out by a "heroic soldier of the caliphate" who attacked the nightclub "where Christians were celebrating their pagan feast."
It said the man fired an automatic rifle and also detonated hand grenades in "revenge for God's religion and in response to the orders" of ISIS leader Abu Bakr al-Baghdadi.
The group described Turkey as "the servant of the cross" and also suggested it was in retaliation for Turkish military offensives against ISIS in Syria and Iraq.
"We let infidel Turkey know that the blood of Muslims that is being shed by its airstrikes and artillery shelling will turn into fire on its territories," the statement said.
According to the Hurriyet and Karar newspapers, police had established similarities between the nightclub shooting and the high-casualty suicide bomb and gun attack at Istanbul's Ataturk Airport in June and was investigating whether the same ISIS cell could have carried out both attacks.
On Monday, Anadolu said more than 100 ISIS targets in Syria have been hit by Turkey and Russia in separate operations.
Citing the Turkish Chief of General Staff's office, Anadolu said Turkish jets struck eight ISIS targets while tanks and artillery fired upon 103 targets near Al Bab, killing 22 extremists while destroying many structures. The Russian jets also attacked ISIS targets in Dayr Kak, five miles to the southwest of Al Bab.
The Associated Press contributed to this report.