Two girls were also involved with the attack directly
Police Bureau of Investigation (PBI) has said a total of 13 people, including two girls, were involved in setting fire to Alim examinee Nusrat Jahan Rafi.
"Till now, police have arrested seven people in connection with the incident," Banaj Kumar Majumder, deputy inspector general and chief of PBI, said at a press conference held at PBI's headquarters, in Dhanmondi, around 1:30pm Saturday.
The investigation into the case - lodged by Nusrat's brother Mahmudul Islam with Sonagazi police station that was later handed over to PBI - is on-going, the PBI chief said.
"We are on the hunt to arrest the rest of the people," Banaj said.
The arrested people are: Sonagazi Islamia Fazil (Degree) Madrasa Principal Md Sirajaddaula, 45, Nuruddin, 20, Sonagazi Senior Fazil Madrasa unit Chhatra League President Shahadat Hossain Shamim, 20, Sonagazi Municipality Councillor and Feni Awami League leader, Moksud Alam, 45, Jobayer Ahmed, 20, Alim examinee and Nusrat's batchmate, Jabed Hossain, 19, and English Department teacher, Absar Uddin, 35.
The whole incident was pre-planned.
According to what the police have unearthed till now, a group of those involved, including Nuruddin, Shamim, Jabed, another accused, Hafez Abdul Kader, hatched the plan to set Nusrat ablaze, April 5.
They made the plan after paying a visit to Md Sirajaddaula in jail, on April 4. Sirajaddaula was in jail following Nusrat's sexual harassment case against him, filed on March 27.
Among the arrested, Shahadat Hossain Shamim was one of those present while setting Nusrat ablaze on the rooftop of a cyclone shelter, adjacent to the madrasa.
One of the girls involved with the incident is currently in police custody, the PBI chief said.
"She, too, was directly involved with the incidents on April 6," he said. "She brought the kerosene and three burqas to Shamim on the rooftop."
The other girl was responsible for calling Nusrat up to the rooftop, Banaj added.
The PBI chief has said there are two main reasons behind the attack.
"One reason was the apparent 'disrespect' Nusrat had shown towards the madrasa principal - thus the whole Alim society - by filing a case against him," Banaj furthered.
Nusrat had also previously spurned one of the main instigator Shamim's advances, which is another reason why Shamim directly participated in the vicious attack.
Earlier, PBI arrested Shamim in Muktagacha upazila of Mymensingh on Saturday morning.
On Friday, Jabed and Nuruddin were arrested in Rampur upazila of Feni and Mymensingh, respectively.
Moksud Alam, a councillor of Sonagazi Municipality and acting general secretary of Awami League's local unit, and also a member of the governing body of Sonagazi Senior Fazil Madrasa, was arrested in Dhaka, Thursday night.
On April 6, Nusrat was set afire, allegedly by people loyal to the principal of her madrasa after he was arrested and subsequently suspended, after she accused him of sexually harassing her.
Nusrat lost her battle for life on Wednesday night, five days after the incident, at Dhaka Medical College and Hospital.
The incident has sparked mass outrage across the country, with people from all walks of life staging demonstrations since Nusrat's death, demanding justice for her murder.