Family members of the Turkish gunman who shot dead Russian ambassador Andrei Karlov have been released from police questioning.
A number of relatives of Mevlut Mert Altintas were taken into custody earlier this week as police attempted to establish the background to the shooting.
Karlov, the ambassador to Turkey, was shot in the back by Altintas, himself a member of security, as the Russian was giving a speech on Monday.
The Turkish policeman who assassinated Russia's ambassador was unlikely to have acted alone, a senior Turkish government official said.
The "well-planned" killing was "fully professional, not a one-man action", the official, who spoke on condition of anonymity, added.
Turkish authorities have not publicly released any information on the policeman's possible motive.
Turkey and Russia, which have backed opposing sides in the Syrian war, vowed not to let the killing disrupt conciliation efforts.
"It was like a movie", says Burhan Ozbilici, who captured the moment Mevlut Mert Altintas shot and killed Andrey Karlov.
Andrey Karlov has been killed in a gun attack at a photo exhibition in the Turkish capital Ankara.