The Mumbai police cyber crime cell is now investigating the terror e-mail sent by the Indian Mujahideen to various media organisations minutes before the blast. The mail was reportedly sent through a cracked wi-fi account from the Chembur suburb of Mumbai. The mail sent from email@example.com, virtually challenged the security agencies to "do whatever you want and stop us if you can".
Meanwhile, the police in Delhi, Gujarat and Rajasthan are looking at links between the Delhi blasts and the terror attacks in Jaipur and Ahmedabad.
The Indian Mujahideen is understood to be staffed by activists of the banned Students Islamic Movement of India (SIMI) and intelligence agencies are also probing that angle.
Forensic teams in Delhi are trying to determine the contents of the bombs. Sources say the bombs used ammonium nitrate with fuel oil, and were packed with metal ball bearings for maximum impact.