Arshad was arrested from east Champaran district after Imtiaz named him during questioning. "He has confessed to participating in the blasts in Kerala and Ranchi," the official added.
The state BJP, meanwhile, formally sought a high-level inquiry into the "slack security arrangements" for the rally, alleging that it was "deliberate".
In a memorandum submitted to the governor DY Patil, the party said, "Nitish Kumar's aversion for Modi is well-known. It appears that the security lapses were deliberate". Despite warnings by the central security agencies, the state government failed to act, the party said.