An Interior Ministry official said that a pair of senior police inspectors have been given the task of finding out if any officers assisted the suspects, reports FoxNews.
In April, three Christians were tied up, repeatedly stabbed and had their throats cut in a Protestant publishing house. The trial of five men accused of the murders began last month but was adjourned until 14 January as defence lawyers requested more time to prepare their arguments.
The investigation was launched after some newspapers alleged police collusion with the killers.
Two suspects, Abuzer Yildirim and Salih Guler were quoted by Radikal newspaper as saying that another suspect, Emre Gunaydin, had told them that he had met with police officials who gave him the locations of Christian churches in the city.
According to Radikal, Yildirim said, "I asked him [Gunaydin] who are the police chiefs that you are speaking to, he said: 'Don't ask, take it easy."'
Allegations of police collusion also arose following the murder in January of Hrant Dink, an ethnic Armenian who roused the ire of Turkish nationalists when he describe the killings of Armenians in the early 20th century as genocide -Turkey has always denied genocide.
According to FoxNews, some believe the authorities failed to act on reports of a plot to kill Dink, although no evidence has linked any government or police officials to Dink's murder.
There are fears that a "deep state" may exist in which a network of informers and ex-officials are linked to organised crime that sometimes targets reformers and other "enemies" of Turkish nationalism.
In addition, Christian leaders in the country have expressed concern that nationalists are promoting hostility against non-Turks and non-Muslims by exploiting the uncertainty of Turkey's place in the world, reports FoxNews.