Prosecutors have revealed new information on Adnan Oktar, a cult leader who faces charges of running a criminal gang.

An indictment against Oktar, who is among 171 defendants detained in an investigation into his cult, said he escaped prosecution earlier thanks to the Gülenist Terror Group (FETÖ).

The indictment added that an investigation was opened into his cult in 2007 but "some people who were later arrested on charges of FETÖ membership changed the accusations in the case and eventually closed it in 2013."

Oktar was arrested last year, along with dozens of his followers and aides, in a criminal investigation. The indictment also includes charges against 55 other defendants, who are either fugitives or have been released pending trial.

The indictment against Oktar and his cult lists a series of charges, ranging from military espionage, organizing a criminal gang, sexual abuse, blackmailing, persecution, bribery, attempted murder, membership of an armed organization and forgery.

Oktar, who owns a TV channel, was a household name in the 2000s but his prominence dates back to the 1980s when he was arrested for "promoting theocracy" for his Islamic views. He resurfaced in 1999 when he was charged with blackmail although he was found mentally ill by a court and spent months in a psychiatric hospital before his release. He made a comeback with a series of anti-evolution books and launched a TV station in 2011.

Prosecutors say FETÖ's involvement in the Oktar case started in 2008 when Tarkan Yavaş and Halil Hilmi Müftüoğlu, two lawyers who served in Oktar's cult, met Zekeriya Öz, a notorious prosecutor who was behind "Ergenekon," a sham trial organized by FETÖ infiltrators in the judiciary and police to ensnare critics of FETÖ.

Following that meeting with Öz, who is currently wanted for FETÖ membership, the investigation against Oktar changed course and was concluded without any detentions, prosecutors say.

FETÖ, which was behind 2016's deadly coup attempt, is known for having a large number of infiltrators in the judiciary, law enforcement, military and bureaucracy. It is already implicated in multiple cases of sham trials run by its members.