In a major breakthrough, the National Investigation Agency has arrested four persons, including alleged mastermind Hyder Ali alias 'Black Beauty', in connection with the Patna serial blasts ahead of Narendra Modi's rally last year. Besides Ali, the others arrested from Ranchi were Taufeeq Ansari, Mojibullah and Numan Ansari, NIA sources said today. NIA had announced a cash reward of Rs five lakh on their head.