Ganajagaran Mancha spokesperson Imran H Sarkar was released on Wednesday night hours after his detention from the city's Shahbagh area.
He was freed around 11:00pm following interrogation, said Rapid Action Battalion (RAB)-3 commanding officer lieutenant colonel Emranul Hasan.
Earlier, the elite force members detained the Ganajagaran Mancha, a platform of secular youths who had organised a mammoth rally at Shahbagh Square primarily seeking capital punishment for ‘war criminals’ in 2013, spokesperson in the afternoon.
Witnesses said when Imran and his supporters were gathering in front of the National Museum for holding a rally around 4:30pm protesting the killings in the ongoing anti-drug drive, RAB members picked him up, dragged him into their van and dispersed his supporters.
With the killing of two people early Wednesday, the number of those killed has risen to at least 137, during the anti-narcotics drives across the country since 14 May.
Shahbagh police station officer-in-charge Abul Hossain said Imran H Sarker and his followers had no permission to hold any programme there.