Turkish authorities have issued an arrest warrant for a retired colonel who has been located in the occupied north, as part of a reopened investigation into the death of a Turkish intelligence officer in a Silivri prison in 2011.

Hasan Atilla Ugur, a retired colonel who once served in Turkey’s gendarmerie’s technical intelligence department, is one of four suspects named in detention warrants issued by the Silivri chief public prosecutor’s office.

The other three, Hasan Ataman Yildirim, a fellow prisoner of the deceased, along with the former Silivri chief prosecutor Ali Isgoren and former prison prosecutor Necip Dogan, were taken into custody during operations in Istanbul and Ankara.

Legal proceedings to locate, arrest and return Ugur from the north to Turkey are under way, according to Turkish reports.

The warrants relate to the death of Kasif Kozinoglu, a former officer with Turkey’s national intelligence organisation (MIT), who died at Silivri state hospital on November 12, 2011, while being held under the Ergenekon investigation. The investigation alleged a clandestine ultra-nationalist fifth estate operating within the military and state apparatus that plotted to overthrow the government.

His sentence was subsequently overturned on appeal, with an acquittal following a retrial in 2019, and went to serve as deputy chairman of Turkey’s Patriotic party (VP).

Kozinoglu, who had returned from Afghanistan shortly before his arrest, collapsed after exercising and showering in his prison ward.

The official cause of death was recorded as a heart attack, though his family disputed the finding at the time, saying he had no known heart problems.

Turkish Justice Minister Akin Gurlek said the case had been reopened following a review, which overturned an earlier decision to close the investigation.

Ugur, who shared a cell with Kozinoglu during the Ergenekon trial, gave an account to Turkish media of the hours before his cellmate’s death, saying the two discussed trial preparations and that Kozinoglu had complained of chest pains after physical exercise.

Ugur also said Kozinoglu had previously told him that a prison faction linked to President Recep Tayyip Erdogan’s rival Fethullah Gulen posed a threat to his life.

An exhumation order has also been issued as part of the renewed inquiry, with samples taken from Kozinoglu’s grave being examined to determine whether he had been administered any other medication while in custody.

Ugur himself was involved in the interrogation of Kurdish militant leader Abdullah Ocalan following his capture in Kenya in 1999.