Police detained a new suspect Wednesday over the December murder of Russian Ambassador to Turkey Andrei Karlov. The suspect, identified as E.B. had phone contact with Mevlüt Mert Altıntaş, the assassin who killed himself when police cornered him.

It is not known where the suspect was detained but the detention was part of an investigation by prosecutors in capital Ankara where Karlov was murdered.

Three others were already remanded in custody over the murder, including two police officers. Altıntaş himself was a riot policeman and was linked to the Gülenist Terror Group (FETÖ), which has been blamed for the July 15 coup attempt. FETÖ is known for its widespread infiltration of the law enforcement and other police officers remanded in custody are believed to be affiliated with the terrorist group.

Karlov was speaking at the opening of an exhibition in an art gallery while Altıntaş, dressed in a suit, sneaked in by showing his police ID though he was off-duty, and started shooting. Karlov was killed on the spot while Altıntaş fled to another floor of the gallery and was killed in a shootout with his colleagues.

The incident rocked Turkey as it was trying to restore ties with Russia following a crisis over the downing of a Russian jet for violating Turkish airspace. Moscow and Ankara later assured it would not harm relations.