They were taken into custody after a raid in the Mirzangal area of the city on Wednesday night, said RAB-9 Media Officer Additional Police Sub-Inspector Md Moniruzzaman.
Pijush Kanti Dey, the former joint convener of Sylhet Metropolitan Chhatra League, had been accused of various crimes, including extortion and violence, according to the law enforcers.
He had been carrying out these activities from his Mirzangal ‘base’, according to some locals.
The three others have been identified as Bappa Pal, Mintu Rai and Raihan Ahmed.
A special RAB-9 team raided Pijush’s office in Mirzangal area on Wednesday night and made the arrests, said SI Moniruzzaman.
A revolver, two rounds of bullets and a ‘massive amount’ of the methamphetamine-based yaba tablets have been recovered from the spot, according to the RAB official.