Banaj Majumder, a deputy inspector general heading the Police Bureau of Investigation or PBI, briefed the media on Saturday about the findings in investigation into the sensational case.
Nusrat, 18, before her death on Apr 10, said she went to the madrasa to sit for Alim exams, equivalent to HSC, on Apr 6.
Four burqa-clad people, who had their faces covered by niqab and hands with gloves, poured kerosene on her and set her on fire when she refused to withdraw the sexual charges against Siraj, she added.
Siraj was already in jail in a case over the alleged sexual harassment of the girl when she came under attack.
DIG Majumder said Nur Uddin, 20, a student of the madrasa and close associate of Siraj, met the principal in jail where the student received “some instructions” from Siraj on Apr 4.
Police believe the attackers plotted the assault following the instructions from Siraj, according to the PBI chief.
HOW THE ATTACK UNFOLDED
Nur Uddin met students Shahadat Hossain Shamim, Jabed Hossain, 19, Abdul Quader and another person at the madrasa hostel on Apr 5 after the meeting with the principal.
“They plotted to burn Nusrat to death and fixed their duties in the attack in the meeting at the hostel,” Majumder said.
Shamim got involved in the attack because Nusrat had earlier refused his proposal for a romantic relationship, Mujumder said and added it was the other reason behind the attack.
One of the female suspects supplied kerosene and burqas to Shamim, according to Majumder.
Shamim, the female suspect and two others then took position on the roof of the madrasa to carry out the attack, the police officer said.
Two of the four assailants entered the madrasa, entry to which was restricted due to Alim exams, as students of a coaching programme that was held from 7am to 9pm.
Another female student gave Nusrat the false information that Nishat was being beaten on the roof.
When Nusrat rushed to the roof, the four attackers tied her using a scarf and set fire on her.
One of the attackers was being called ‘Shompa’ by the others and police arrested Siraj’s niece Umme Sultana Poppy in the hunt for ‘Shompa’.
One of the four assailants and one of the two female suspects were in police custody, Majumder said but declined revealing their names.
He said Shamim was under police watch.
Jabed was in remand with another student, Jobayer Ahmed, 20.
Police also remanded teacher Afsar Uddin, 35, and local ward councillor Maksud Alam, 45, over the killing of Nusrat.
Hafez Abdul Quader is the only one accused still on the run in the murder case. Nusrat’s brother named eight suspects in the case.