Along with Mutlu, 11 other suspects -- including seven governors, a deputy governor and three district governors -- were detained for being members of the Fethullah Terror Organisation, Xinhua news agency reported.
Fethullah Gulen, a Turkish cleric based in the US since 1999, has been accused of plotting the military coup attempt, in which at least 239 persons were killed.
Mutlu, after serving four years as Istanbul governor between 2010 and 2014, had been working with the Interior Ministry.
He was suspended from his position following the failed coup and detained on July 26 in the investigations into the plotters.
During his interrogation, Mutlu had denied having ties with Gulen's organisation, Anadolu said.
"On the coup attempt night I condemned the coup on Twitter and I obviously said they should pay the price before law," he said.
Mutlu confessed he had once spoken to Gulen over the phone but never met him, Anadolu noted.
Two books written by Gulen were seized in Mutlu's house, while the phone number of former Air Force Commander Akin Ozturk, who was arrested and dismissed from the Turkish Armed Forces over his link to Gulen's group, was found in his phone, according to the agency.
In his testimony, Mutlu said the books belong to his sister-in-law or her son, and the phone number of Ozturk existed because of their prior professional relationship in the southeastern city of Diyarbakir between 2007 and 2010.
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