Mr Islam was taken into custody from near the Paroma Island on the Eastern Metropolitan Bypass after CPI(M) demanded his arrest for masterminding the attack on Mr Mollah at Kantatala, police said.
Mr Mollah, who was attacked on January 6, is admitted to a private hospital in Kolkata.
Mr Islam was admitted to a private nursing home at Rajarhat on January 8 after CPI(M) cadres allegedly fired at his vehicle and attacked him at Bamanghata in the district.
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