Investigators are piecing together a portrait of the gunman who opened fire in a popular Istanbul nightclub just after midnight on New Year's Eve.
The man is believed to have links to the so-called Islamic State militant group, which has now claimed reponsibility for the attack.
Turkish media have also quoted police sources saying the man may be from the Central Asian countries of Uzbekistan or Kyrgyzstan.
But while a number of others have been arrested in connection with the shooting, the gunman himself remains at large.
Turkey's deputy prime minister, Numan Kurtulmus, says authorities are getting close to identifying the prime suspect.
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"Eight people have been detained. Information about the fingerprints and basic appearance of the terrorist have been found. In the process after this, work to identify him swiftly will be carried out. We hope we will find not only the terrorist, but also his connections and those who gave him support, inside and outside the club."
The Reina nightclub's owner says he is surpised the shooter managed to get a gun into the club, given Turkey's high-security environment.
"How did he manage to come despite all the intelligence and all the security measures? I can only call this creature a demon -- I can't even say he's a terrorist -- I don't know how he managed to come to the club."
A statement released on the so-called Islamic State's social media said the attack was carried out by what it called a "heroic soldier of the caliphate".
It explained the nightclub was targeted because it was a place where Christians celebrate their holiday.
But Ravza Kavakci, an MP in Turkey's ruling AK party, says most of the victims were Muslim.
"The people who lost their lives, the people who are in the hospital - there are Saudi citizens, among them. They are mostly from Arab countries, they are Muslims!"
IS media also said the New Year shooting was a response to Turkey's military incursion in Syria.
That operation began in August, designed to push militants away from the Turkish border.
Turkish authorities say it isn't yet clear whether IS really did commit the attack, or was merely claiming it for publicity.
One mourner in Istanbul said Turks would continue to stand up to terrorism.
"They shouldn't intimidate us. We must not be afraid. Because we will die as long as we are afraid and as long as we keep silent. We don't want to die any more."
Turkey remains in a state of emergency, which was declared following a failed military coup in July.
The country has experienced a wave of violent terror attacks this year, blamed on both IS and Kurdish separatists.
Turkey's deputy prime minister Kurtulmus says this latest attack is an effort to drive a wedge through Turkish society.
"With this terrorist attack, unfortunately, they try to create divisions among the public over different lifestyles, religions and sects."
Turkish police have released blurry CCTV images of the suspect.
One shows the man entering the club with a long-barrelled weapon, believed to be a Kalashnikov automatic rifle.
The search continues.
