The protestors also set fire to some wooden articles kept in the police station premises which fire brigade personnel later doused, official sources said.
The agitators also jammed roads and burnt tyres and chased away Deputy Collector of Land Reform, Virendra Kumar.
They are residents of Toigarh village, from where the liquor trader Mukesh Kumar hails.
No personnel was present at the Barbigha police station at the time as the new set of officials was yet to assume duty.
Over a dozen officials of the police station and the superintendent of police Babu Ram was transferred yesterday on the orders of Chief Minister Nitish Kumar.
The trader was picked up by the Barbigha police station and beaten up severely and taken to the office-cum-residence of the former SP Babu Ram on January 25. When his condition deteriorated, he was admitted to PMCH late that night.