By Serdar Acil and Zafer Fatih Beyaz

ANKARA

A former Turkish civil servant and suspected senior member of FETO -- the group behind the July 2016 defeated coup -- was arrested on Thursday in connection with the assassination that December of Russia’s ambassador to Turkey.

Security units in the capital Ankara arrested an individual identified as S.S., formerly employed by the Turkish Information and Communication Technologies Authority (ICTA), also identified as a senior Fetullah Terrorist Organization (FETO) member and the superior of Mevlut Mert Altintas, the Russian envoy’s late assassin.

Andrey Karlov was assassinated at an Ankara art gallery on Dec. 19, 2016 by Altintas, an off-duty police officer linked to the FETO terrorist group who was shot dead by police that day.

On Monday, prosecutors issued arrest warrants for eight people, including FETO terror group leader Fetullah Gulen, over possible links to the assassination.

The suspect S.S. was found to be a user of ByLock, an encrypted cellphone app used by coup-plotters, said a security source, who asked not to be named due to restrictions on speaking to the media.

The suspect is also believed to be responsible for deleting Altintas's e-mails and for conveying the terror group's instructions to him and organizing the assassination, added the source.

In January, another former ICTA civil servant was arrested and remanded in custody on charges of association in plotting manslaughter, according to security sources.

Late last year, six people were arrested over the assassination, including three police officers, Guru Media Broadcast Group Chairman Hayreddin Aydinbas, and Mustafa Timur Ozkan, who organized the art exhibit.

FETO and its U.S.-based leader Fetullah Gulen orchestrated the defeated coup of July 15, 2016, which left 250 people martyred and nearly 2,200 injured.

Ankara also accuses FETO of being behind a long-running campaign to overthrow the state through the infiltration of Turkish institutions, particularly the military, police, and judiciary.