Bangladesh, Nov. 11 -- The deadly explosion that ripped through a busy area of Delhi on November 10 has shaken India, ignited a nationwide political and security response, and renewed long-standing anxieties about terror networks operating across the country. With 12 people killed and around two dozen injured, the blast has triggered a sweeping investigation under Indias strict anti-terrorism laws, bringing central agencies, state police units, and intelligence bodies into what Prime Minister Narendra Modi describes as an urgent quest for justice.

Speaking from Bhutan, where he was on an official visit, Modi condemned the “horrific” attack and vowed that Indias security and intelligence agencies would uncover the conspiracy b...