NIA had sought ten-day remand of the accused but Principal Judge P B Desai of the NIA court remanded them in the agency's custody until next Tuesday after hearing arguments submitted by the prosecution and defence.
Police arrested Inayat Haji Patel, Mohammad Yunus Shaikh, Abdul Samad and Abid Patel in connection with the double murder in November.
Seeking the ten-day remand, NIA contended that it needed to find out more about Abid's links on the basis of his call data records.
Abid is the brother of the prime accused in the case Javed Chikna, also an accused in the 1993 Mumbai serial blasts case, and believed to have fled from the country many years back.
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Abid, a British citizen, was arrested in a joint operation by the state Anti Terrorist Squad and various central agencies early this month from Indo-Nepal border.
NIA said two SIM cards were found from Abid and it was necessary to extract details about his contacts.
They argued that Bharuch police had investigated this angle in the past as all the four accused were in their custody then.
The BJP leaders, identified as Shirish Bangali, ex-party president of Bharuch district and senior RSS member, and Pragnesh Mistry, general secretary of Bharatiya Janta Yuva Morcha of the district, were shot dead in Bharuch on November 2.
The initial investigation was conducted by Bharuch police and state ATS. The state police had termed the double murders an 'act of terror'.
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The NIA has alleged the contract for killing the BJP leaders was given by Javed Chikna, another aide of Dawood and an absconding accused in the case, apparently to avenge communal riots in Mumbai and in Gujarat in 1993 and 2002, respectively.
One of the charge-sheeted accused, Abid Patel, is brother of Javed Chikna, who is also wanted for the 1993 Mumbai bomb blasts.