Sheikh Mohammad Golam Mostafa, officer-in-charge of Chandrima Police Station, said they detained raiding different student messes.
The video clip of the incident is being scrutinised and those will be found innocent will be released, he said.
A group of ‘BCL activists’ threw Rajshahi Polytechnic Institute Principal Farid Uddin Ahmed into the pond on the campus on Saturday afternoon for his refusal to allow two students, including joint general secretary of the institute unit of BCL Kamal Hossain Sourav, to fill up forms for examination for inadequate class attendance.
The incident was captured in a surveillance camera.
It was seen in the video footage that at least 10 people were taking the principal towards the pond. Some of them were holding his hands while some others were pushing him from behind.
They threw the principal into the pond within seconds and fled the scene.
Later, other students, officials and employees of the institute rescued him.
Principal Farid Uddin filed a case with Chandrima Police Station at night over the incident.
The accused include Sourav, Murad, Shanta, Bony, Hasibul Hossain Shanta, Salman Tony, Habibul and Maruf.
Meanwhile, the students and teachers of the polytechnic institute on Sunday staged demonstrations in front of the main gate of the institute to press home their six-point demand, including immediate arrest of those involved in the incident and their exemplary punishment.
They took to the street around 11am and formed a human chain on the road.
The other demands include cancelling the studentship of the offenders, taking steps to stop student politics on the campus, stopping entry of the outsiders into the campus, and ensuring security of all on the campus and a healthy education environment.
Additional police were deployed on the campus to avert untoward incident.
Meanwhile, Rajshahi city unit BCL condemned the incident.
In a press release, Rocky Kumar Ghosh and Mahmud Hasan Rajib, president and general secretary of the unit, said a six-member committee was formed to look into the incident and the committee was asked to submit its report within three working days.