Akhtar was arrested along with Bhatkal on the India-Nepal border last month.
He revealed before the investigators the details of the places they visited in Hyderabad before carrying out the blasts.
The twin blasts at the crowded Dilsukhnagar market claimed 18 lives.
The NIA is investigating if Akhtar and Bhatkal received any local help in the terror attacks.
Bhatkal and Akhtar, allegedly involved in several bomb blasts in different parts of the country, were arrested by Bihar police on the India-Nepal border Aug 28. The NIA later brought them to Delhi and interrogated them.
The terror suspects reportedly confessed their role in Dilsukhnagar blast. They allegedly planted explosives on two bicycles.
According to Hyderabad police, the profiles of the two suspects seen in the CCTV footage before the blasts match with Bhatkal and Akhtar.