A suspect already jailed for membership to the Gülenist Terror Group (FETÖ) was re-arrested for involvement in the murder of Andrei Karlov, the slain Russian Ambassador in Ankara. Karlov was assassinated in November 2016 by Mevlüt Mert Altıntaş, an off-duty police officer with links to the ubiquitous terrorist group which is also blamed for the July 15 coup attempt two years ago.

The suspect, identified with his initials V.K.A., is being charged with complicity in the murder and authorities say he had "a key role" in the murder that shook relations between Turkey and Russia. The suspect was a user of ByLock, an encrypted messaging app exclusively used by the terrorist group and was dismissed from his job in the public sector after the coup attempt.

In a related development, investigators questioned a doctor as a witness again for giving a report that granted Mevlüt Mert Altıntaş a day off. The doctor said Altıntaş was suffering from diarrhea. An investigation showed the suspect looked up online on "how to get diarrhea," to have the day off to get to the art gallery in Ankara to kill Karlov.

Karlov was speaking at the opening of a Russian-themed exhibition in an art gallery in Çankaya, Ankara when he was shot dead by Altıntaş. Altıntaş was killed in a subsequent shootout with police inside the gallery.

The assassination was at a time of thawing in strained Turkish and Russian relations and an investigation found that Altıntaş was linked to FETÖ, which tried to portray the murder as the work of an extremist group.

Since the murder, Ankara and Moscow have gradually made progress in rebuilding ties that were derailed by the 2015 downing of a Russian fighter jet over the Syrian border by the Turkish military.

Prosecutors say Altıntaş personally knew Fetullah Gülen, the U.S.-based leader of the terrorist group. Five people including three police officers were arrested in the probe in the killing of Karlov.

After Karlov's assassination, a concurrent investigation was initiated by Turkey and Russia to find out the motives behind it. Altıntaş's hard disk was examined, first by Turkish authorities and then by the Russian delegation, who took it to Russia, explaining that they wanted to study the disk using alternative methods, which eventually recovered deleted files.

The Russian delegation found that two files with the words "Fetullah Gülen" present, 690 files with "Hizmet," a term that means "service" and it is also what FETÖ calls itself. Also, four files with the words "FETÖ," and one file with "Nur Community" were deleted from Altıntaş's computer.

They also searched for the words "al-Qaida", "al-Nusra" and "Daesh" in the deleted files, but no files were found with these words, the Hürriyet daily reported.