Censor.NET reports citing Aljazeera.
"The terrorist actually said that he did it," Istanbul Governor Vasip Sahin told journalists Tuesday, CNN reports.
According to him it was "clear that this was carried out in the name of Daesh."
Turkish media reported the killer was captured with his four-year-old son, but the governor said the child was not present during the police raid.
Police confiscated $197,000, two weapons and ammunition clips at the apartment.
The state-run Anadolu Agency said a man from Kyrgyzstan and three women - from Somalia, Senegal and Egypt - were also detained in the raid.
Earlier, BBC said of 39 killed and 70 wounded in New Year's night attack on the Reina night club in Istanbul where a man opened fire during a New Year celebration to kill dozens.
As reported, ISIS claims responsibility for the attack.