Justice Minister Akın Gürlek said Sunday that the state would pursue those responsible at all costs as an investigation into the 2009 death of politician Muhsin Yazıcıoğlu deepened.

Earlier this week, 29 suspects were detained, 19 of whom were arrested, as part of a probe focusing on the Gülenist Terror Group’s (FETÖ) alleged role in the helicopter crash that killed Yazıcıoğlu.

Yazıcıoğlu, the chair of the Great Unity Party (BBP), was known for his opposition to the terrorist group, which at the time portrayed itself as a charity movement. Yazıcıoğlu’s family has claimed that FETÖ played a role in his death, and a renewed investigation has focused on allegations that F-4 fighter jets piloted by FETÖ-linked officers caused the crash by flying too close to the helicopter before the accident in southern Türkiye’s Kahramanmaraş province. Yazıcıoğlu was on an election campaign tour when the helicopter crashed into a snow-covered mountain, killing him, his aides and a journalist.

Ali Armağan and his wife, Şerife, were among the suspects detained earlier this week. Investigators discovered several links between the couple and FETÖ, although they flatly denied the charges. Armağan was the pilot of one of the F-4 jets flying near the helicopter, but he denied the charges. Investigators discovered that he had contacts with several top FETÖ figures, including Adil Öksüz, one of the fugitive masterminds of FETÖ’s 2016 coup attempt who was in charge of the group’s military infiltrators. Şerife Armağan’s fingerprints were also discovered in a book found at Öksüz’s residence after he disappeared in 2016. Media reports say that a phone number belonging to Ali Armağan was involved in 152 calls with Öksüz between 2012 and 2014.