Shyamal Karmaka was arrested from Rampurhat in the early hours of today and is being interrogated, North 24 Parganas Additional Superintendent of Police Bhashkar Mukherjee said.
A total of nine persons, including Karmakar's sister, have so far been arrested, he said.
Amal Barui and Bhuban Saha, who were members of the group of people who killed the 21-year-old student, Sourav Chowdhury, were arrested yesterday.
During interrogation, the duo revealed that they had kidnapped Sourav from near his home and strangled him before hitting him on the head with a heavy object on July 5.
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Five persons were arrested in this connection on July 7 last.
Among the five was Polly Maity, the sister of Shyamal Karmakar. She was arrested for giving shelter to the accused.
Anup Talukdar, one of the accused named in the FIR, was arrested in a raid on July 6.
Sourav was killed for starting a drive against hooch dens in the area allegedly run by Karmakar.