Five blasts ripped through the capital on the evening of September 13 last year, for which terror group Indian Mujahideen had claimed responsibility.
Indina Mujahideen, the terror group admitted being responsible for the Sep 2008 Delhi blast.
A senior police official said everything possible was done to catch those involved in the blasts, including Indian Mujahideen chief Amir Raza Khan.
Police had caught 12 suspected men and killed two in an encounter in south Delhi's Jamia Nagar flat, a week after the explosions.
Police believed that Pak-based Lashkar-e-Taiba militant outfit aided the Indian Mujahideen in the blasts.