By Sarah Rainsford
BBC News, Istanbul
A senior Turkish policeman has been suspended amid allegations police had advance warning of the murder of ethnic Armenian journalist Hrant Dink.
Dink had angered Turkish nationalists
Ten officers and paramilitary policemen have already been suspended in the Black Sea city of Samsun.
They were suspended after video images were leaked to the press showing officers posing with a teenager who confessed to the murder.
Mr Dink was shot outside his newspaper office on 19 January.
The inquiry into the official handling of the case has raised serious questions over the possible complicity of Turkey's security forces with extreme nationalist groups.
Hrant Dink had angered Turkish nationalists by challenging the state position that the mass killing of Ottoman Armenians by Turks in WWI was not genocide.
Investigators are looking into allegations that Istanbul police were informed that Hrant Dink's life was in danger eleven months before he was killed.
Reports in the Turkish press say the head of police intelligence here admits receiving a letter from police in the city of Trabzon last February with a tip-off from an informer.
The teenager who confessed to killing Hrant Dink is from Trabzon.
The suspect posed with a Turkish flag next to security officials
The reports say the Istanbul police intelligence chief made only superficial inquiries and failed to pass the information on to his superiors.
Police sources have confirmed to the BBC the officer concerned has now been suspended from duty while the investigation continues.
The focus now appears to be on whether or not the failure to act was deliberate.
For days a fierce debate has raged about possible links between those who killed Hrant Dink and ultra-nationalist networks operating with the state and security forces.
For many those suspicions hardened when video footage was released showing police officers posing alongside the main suspect in the murder.
Prime Minister Recep Tayyip Erdogan has fuelled that debate by alluding to what is known here as the "deep state" twice since Mr Dink's killing.
He has talked of dark structures operating within the state but outside the law in the belief they are protecting the country.