The suicide bomber who claimed the lives of four people and injured 36 on Istanbul's well-known İstiklal Avenue on Saturday had fought in DAESH ranks in its stronghold Raqqa and Deir ez-Zor in Syria, Turkish media reported.According to testimony from his parents, Mehmet Öztürk, who was born in southeastern Gaziantep province in 1992, was rendered insane due to a traffic accident. His father, Nahsen Öztürk, who is a factory worker, said in his testimony that his son left Gaziantep in 2013 and went to Istanbul.

His father also said that he filed a missing person's report with the police after his son said that he had joined DAESH in Syria in one of the rare telephone conversations they had. Öztürk reportedly did not have any criminal record prior to the bombing. This is thought to be a significant reason for his being chosen as a suicide bomber since DAESH is reported to have previously instructed non-recorded militants in its ranks to take part in suicide attacks after intensified police raids.

According to information from local sources, Öztürk crossed the Syrian border in 2013 from the Çobanbey border crossing in his hometown and fought with opposition ranks in Aleppo against regime forces for eight months. Then he joined DAESH in 2014 and served in the terrorist organization's battles against the PKK affiliate Democratic Union Party (PYD), which included fighting in Raqqa and Deir ez-Zor. After meeting with his family in Gaziantep three months ago and returning to Syria, he allegedly crossed the border to Turkey at Çobanbey and stayed in Gaziantep and Adıyaman provinces for a couple of days. Investigators have revealed footage of Öztürk buying a bus ticket for Istanbul in Adıyaman on March 18. They also uncovered that he came to Istanbul on the day of the attack on a bus. A footage showed Öztürk following an Israeli tourist group after they left their hotel in Beşiktaş to go to a restaurant for breakfast. After waiting for their exit on a side street, Öztürk blew himself up.