This still photo, taken from surveillance footage and released on Monday, January 2, is believed to show the gunman responsible for carrying out a New Year's Day attack on the Reina nightclub in Istanbul. The popular nightclub was attacked shortly after midnight on Sunday, January 1. At least 39 people were killed and 69 were wounded, Turkey's Interior Minister said. Authorities are still searching for the attacker. HANDOUT/AFP/Getty Images

A Turkish special forces officer stands near the Reina nightclub on January 2. ISIS claimed responsibility for the attack in a statement posted to Twitter. OZAN KOSE/AFP/Getty Images

A friend of someone killed in the attack reacts near victims' pictures outside the nightclub on January 2. OZAN KOSE/AFP/Getty Images

A police officer inspects cars near the scene on January 2. Halit Onur Sandal/AP

People carry the coffin of Yunus Gormek, a victim of the attack, during a funeral ceremony in Istanbul on January 2. BULENT KILIC/AFP/Getty Images

People mourn outside the Forensic Medical Center in Istanbul on January 1. Suleyman Kaya/DHA/Depo Photos/AP

Relatives of Ayhan Arik, one of the victims of the attack, cry during a funeral ceremony in Istanbul on January 1. OZAN KOSE/AFP/Getty Images

An ambulance rushes from the scene of the attack on January 1. Halit Onur Sandal/AP

A woman is consoled at the site of the attack. YASIN AKGUL/AFP/Getty Images

Medics wheel a stretcher at the scene. YASIN AKGUL/AFP/Getty Images

Police officers stand guard. Burak Kara/Stringer/Getty Images

People leave the scene of the attack. STR/AP

A medic reacts near the scene of the attack. Burak Kara/Getty Images

A wounded victim is rushed from the scene. IHA/AP

Medics and security officials work at the scene of the attack. IHA/AP

A wounded person is put into an ambulance. STR/AP

People walk in the rain near the scene of the attack. Halit Onur Sandal/AP