The family of the assassin and his roommate were detained for questioning as investigators are looking for possible links to the Fethullah Gulen Terrorist Organisation.
Turkish authorities on Tuesday detained six people linked to the assassin who shot Russia's ambassador to Turkey, Andrey Karlov.
Karlov was shot on Monday evening at the opening of a photo exhibition in the Turkish capital, Ankara.
Turkey identified the killer as 22-year-old Mevlut Mert Altintas, a police officer working for Ankara's riot police for over two years.
Police detained his family and a roommate as they widen the probe into why the off-duty policeman gunned down the envoy.
His mother, father, sister and two other relatives were detained in the western Turkish province of Aydin, while his flatmate in Ankara was also detained, Anadolu Agency said.
Turkey and Russia called Monday's attack an attempt to undermine a recent thawing of ties that have been strained by Syria's civil war.
Altintas was shot dead at the gallery by Turkey's special forces.
Links to FETO investigated
A senior Turkish security official said investigators were focusing on whether Altintas had links to the US-based cleric Fethullah Gulen, who is also the head of the Fethullah Terrorist Organisation (FETO).
Ankara blames FETO for the July 15 coup attempt which left hundreds dead and thousands injured.
Turkish President Recep Tayyip Erdogan said on Monday he and Russian President Vladimir Putin had agreed during a telephone call that their cooperation in fighting terrorism should be even stronger after Karlov's death.
Putin said the attack was aimed at derailing Russia's attempts to find, with Turkey and Iran, a solution to the Syria crisis.
An 18-person team sent by Moscow arrived in Turkey on Tuesday and will work with Turkish authorities to investigate the shooting.
Foreign Minister Mevlut Cavusoglu said the street on which the Russian Embassy is located will be renamed for the ambassador.