Abdulkadir Masharipov is suspected of killing 39 people of different nationalities only two hours into the New Year in the Reina nightclub in Istanbul.
Since being detained by Turkish security forces in a raid on an apartment in Istanbul on 16 January, more information has emerged on who he is and where he came from.
Officials questioning him hope to find out more about cells of so-called Islamic State (IS) in Turkey. The militant group has said it was behind the attack.
Who is he?
According to Istanbul Governor Vasip Sahin, Abdulkadir Masharipov is a 34-year-old Uzbek who speaks four foreign languages - Chinese, Russian, Arabic and Turkish.
Mr Sahin said he had been "very well trained". Officials believe he trained as a militant both in Afghanistan and Pakistan and has contacts inside Syria with IS.
It is believed that Masharipov entered Turkey in January 2016, crossing the Iranian border illegally.
The same route has been used by human traffickers as well as smugglers, especially after the war in Afghanistan.
Radicalisation of young people from Central Asia is not unusual and about 4,000 people are believed to have travelled from the region to Syria in recent years.
A security analyst told the BBC that the suspect might have been hired by IS instead of being radicalised by the group.
Where was he captured?
Police raided a flat in the Istanbul suburb of Esenyurt and detained him and four other people - a man of Iraqi origin and three women from Senegal, Egypt and Somali.
They also found weapons, ammunition, two drones and nearly $200,000 (£164,000).
Masharipov is alleged to have moved to the flat after carrying out the nightclub attack.
It is not yet clear what links, if any, the other people in the flat have to IS.