India, Nov. 21 -- The National Investigation Agency (NIA) on Thursday formally arrested four key conspirators in the November 10 Red Fort blast taking the agency's total arrests in the case to six.

All four - Dr Muzammil Shakeel Ganai of Pulwama, Dr Adeel Ahmed Rather of Anantnag, Dr Shaheen Saeed of Lucknow, and Mufti Irfan Ahmad Wagay of Shopian - had earlier been detained and subsequently arrested by the Jammu & Kashmir Police as part of the nationwide crackdown on the so-called "white-collar" terror module.

Investigators believe each of them played a direct role in planning and executing the suicide attack that killed at least 12 people.

The suspects were taken into custody in Srinagar on production warrants issued by a Patiala Hou...