Turkish-Armenian journalist Hrant Dink was shot dead on Friday in broad daylight near the Istanbul office of his newspaper, Agos.
He had frequently called for the killings of Armenians by Turks during World War I to be called genocide, angering Turkish nationalists.
Supporters gathered later in the day to protest against the killing.
An impromptu memorial was set up to the slain journalist.
Patriarch Mesrob Mutafyan declared 15 days of mourning for the Armenian community.
The alleged killer was identified from CCTV footage.
Teenager Ogun Samast was identified by his father, after he saw his son on the CCTV pictures.
Supporters and friends continue to mourn Hrant Dink, as police question seven people in connection with the killing.
In cities across Turkey - such as Izmir - people are remembering Hrant Dink (photo: Emin Ozkan)