Former journalist Osman Arslan was arrested in the reopened investigation into the death of former MİT official Kaşif Kozinoğlu, who died at Silivri Prison in 2011. Ömer Vatan, who was serving as the prison director at the time, and shift supervisor Kazım Beyke were placed under judicial control in the form of a travel ban.
The investigation conducted by the Silivri Chief Public Prosecutor's Office is continuing on charges of "intentional homicide," "establishing, managing or being a member of an organization formed to commit a crime," and violating Law No. 2937.
After completing their procedures at the gendarmerie, Arslan, Vatan and Beyke were referred to the Silivri Courthouse following a medical examination. Once their statements to the prosecutor were completed, Arslan was sent to the criminal judgeship of peace with a request for his arrest, while Vatan and Beyke were referred with a request for judicial control.
The judgeship ordered Arslan's arrest on charges of "being a member of an organization established to commit a crime" and "disclosing prohibited information for the purpose of political or military espionage." It ordered that a travel ban be imposed on Vatan and Beyke.

Investigation had been reopened
Justice Minister Akın Gürlek said Kozinoğlu had been taken to Silivri State Hospital after falling ill at Silivri No. 1 L-Type Closed Penal Institution, where he was being held in custody on Nov. 12, 2011, and that he was found to have died upon arrival at the hospital.
During the initial investigation, camera footage and medical documents were examined, and statements were taken from prison, gendarmerie and healthcare personnel, as well as Kozinoğlu's cellmates and wife. At the end of that process, a decision of non-prosecution was issued on April 10, 2012.
After the file was reexamined by the Department for the Investigation of Unidentified Crimes, the Silivri Criminal Judgeship of Peace lifted the non-prosecution decision in a ruling dated Aug. 26, 2026, and reopened the investigation. A confidentiality order was issued in the investigation, and a special team was formed.
In the new phase of the investigation, judicial proceedings were initiated against 11 suspects who were working at the penal institution on the day of the incident. Ten of the suspects were detained, while one was determined to be abroad as a FETÖ fugitive.

Number of detainees had earlier risen to six
One of the 10 suspects initially detained was arrested, while nine were released. Judicial control measures were imposed on seven of them. Later, nine more suspects—one reporter, one cameraman and seven healthcare workers—were detained.
Following the procedures involving this group, three suspects were referred to the judgeship with a request for their arrest. A travel ban and an obligation to report were sought for three suspects, including the cameraman, while a travel ban was sought for the other three. The judgeship ordered the arrest of three people, including a reporter, and imposed judicial control measures on six.
As part of the investigation, an exhumation was carried out to determine Kozinoğlu's exact cause of death and whether third parties had intervened in his death.
The screenwriters of the television series Kurtlar Vadisi, Raci Şaşmaz, Bahadır Özdener and Cüneyt Aysan, also gave statements to the prosecutor as people with knowledge of the matter. The Chief Public Prosecutor's Office also decided to examine the series Kurtlar Vadisi Pusu.
Silivri Chief Public Prosecutor Ali İşgören, who was serving at the time of the incident, prison prosecutor Necip Doğan, and Kozinoğlu's cellmates—retired Navy Captain Hasan Ataman Yıldırım and Gendarmerie Colonel Hasan Atilla Uğur—were also detained as part of the investigation.
Doğan and İşgören were arrested. Judicial control in the form of house arrest was imposed on Ataman Yıldırım and Uğur. At this stage, the number of arrested suspects in the investigation rose to six, while the number of suspects subject to judicial control rose to 15.
In subsequent proceedings, former journalist Osman Arslan, ambulance driver Süleyman Kaba, Ömer Vatan and Kazım Beyke were also detained. Kaba was released after giving a statement to the gendarmerie, taking into account the existing evidence.
Enver Altaylı, whose 23-year, four-month prison sentence for "membership in an armed terrorist organization" and "political and military espionage" in a trial under the FETÖ investigation was upheld in 2024, could not give a statement in the investigation because of health problems. It was stated that his statement would be taken if his health improved.