Fahri Sarrafoglu, a journalist, one of 30 initial suspects, was freed after he had been interrogated by a prosecutor in Istanbul. This brought the number of released suspects to twelve in the investigation of the "parallel state," an alleged network of bureaucrats allegedly embedded in the country`s institutions, including the judiciary and the police and linked to the U.S.-based preacher Fethullah Gulen.

Earlier on Monday, Elif Yilmaz, Ebru Senvardar and Naci Celik Berksoy, who all worked on a TV series known as "One Turkey" which is shown on the Samanyolu news and entertainment network, were also released.

In addition, Huseyin Gulerce, a former columnist of the daily newspaper Zaman, was freed after three hours of questioning.

The editor-in-chief of Turkey’s Zaman daily, Ekrem Dumanli, the chairman of the Samanyolu Media Group, Hidayet Karaca, as well as Makbule Cam Alemdag, a scriptwriter of a TV series, which is shown on the network, are still under investigation.

Police asked for one more detention day for the suspects to be interrogated, in case the interrogation might take until the morning.

Producer Salih Asan along with director Engin Koc, and scriptwriters Hikmet Tombulca and Samim Noyan were among those, including Makbule Cam Elamdag, Ahmet Sahin and Ali Kara, who were released late on Dec.15.

All those who have been detained are allegedly linked with Gulen and his so-called Gulen movement. The Zaman daily is also allegedly close to the same movement which the government has described as a "parallel state."

They were charged with forgery, fabricating evidence and forming an alleged crime syndicate to overtake the sovereignty of the state.

The operation was in part generated by a complaint letter filed by the founder of the Tahsiye Publishing House, Mehmet Nuri Turan, who said he had been targeted by U.S. based preacher Fethullah Gulen.

In a speech, the preacher had alleged that Tahsiye and its "Tahsiyeciler" group had links with extremist groups -- including an al-Qaeda faction -- Hezbollah, and the Islamic Great Eastern Raiders Front.

In December 2013, an anti-graft probe targeted a number of high-profile figures, including the sons of three former government ministers and leading Turkish businessmen.

The government denounced the probe as a "dirty plot" constructed by the "parallel state."

Since then, hundreds of police officers have been detained on charges of eavesdropping on Turkey`s top officials, disclosing highly sensitive information, forming and belonging to an organization to commit crime, violating privacy, illegally seizing personal information and the forgery of official documents.

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