A local Bangladesh Chhatra League leader, along with his associates, planned and carried out the attack on the Hindu community in Pirganj upazila of Rangpur last week.
Rapid Action Battalion (RAB) revealed the information during a press briefing in Dhaka on Saturday.
Saikat Mandal, arrested for his alleged involvement in the attack, was a leader of the ruling Awami League-backed students' wing at the philosophy department of Carmichael College.
However, when contacted, Saiduzzaman Sijar, the college unit president of the organisation, said Saikat had been expelled from the organisation on 18 October.
Saikat led the attack on the Hindu village in Pirganj and set their houses on fire, said RAB.
The elite battalion said Saikat provoked the locals by spreading rumours and false posts on Facebook.
On the night of the attack, the 24-year-old student's associate Rabiul Islam gathered the locals after making announcements from the mosque. Then the attack was carried out.
RAB arrested the duo from Tongi on Friday night and held a media briefing on Saturday in Dhaka's Karwan Bazar.
RAB spokesperson Commander Khandaker Al Moin said, "Saikat Mandal had been using social media to spread communal hatred. He had been coming up with various provocative posts since the Cumilla incident."
"He has been instrumental in spreading rumours that led to the attack as Rabiul Islam had cooperated in spreading the statements," said the RAB official.
On 17 October, 18 Hindu houses in Pirganj were set on fire, centering on a Facebook post by a Hindu youth. Police also arrested the youth Paritosh Sarker.
RAB said Saikat had been waiting for a "turbulent time" to destroy communal harmony. Paritosh's Facebook post plus the communal tensions centreing on the Cumilla incident provide him with the "timing".