One of the two youths, caught after the murder of Oyasiqur Rahman Babu, was a JMB activist who was arrested with a huge cache of explosives in Narsingdi a few years ago, said DMP Joint Commissioner Monirul Islam.
But it is yet to be known whether the attack was planned and executed by a single organisation.
“It can be Jama'atul Mujahideen Bangladesh (JMB), Ansarullah Bangla Team or Harkat-ul-Jihad-al-Islami (Huji),” Monirul Islam told The Daily Star.
He added that a “seven-member sleeper cell” had committed the murder. “We don't know how many, but some others outside the sleeper cell were also involved in it.”
Oyasiqur, 27, online activist and blogger, was hacked to death by three cleaver-wielding youths in the capital's Tejgaon Industrial area around 9:00am on Monday.
Of the three, Zikrullah and Ariful Islam were caught by people and handed over to police.
According to sources, Zikrullah is from Gajaria Kandi of Raipura upazila, Narsingdi. Son of madrasa teacher Maulana Mainuddin, he is the eldest of five brothers and two sisters.
Local police said there is no record of his arrest in Narsingdi. “We didn't find any record regarding Zikrullah's arrest here,” said Azharul Islam Sarkar, officer-in-charge of Raipura Police Station, told this correspondent.
“However,” he said, “We will investigate to find more about the boy.”
Zikrullah got admitted to Hathazari madrasa in Chittagong two years back, locals and family members said, adding he was a good boy but “brainwashed” in the madrasa.
Hathazari madrasa is known as the headquarters of Hefajat-e Islam, an Islamist organisation which took to the streets in the capital demanding hanging of “atheist bloggers” after Ahmed Rajib Haider was brutally murdered in mid-February 2013.
Monirul Islam, who leads militancy investigations, said they were yet to be sure whether Zikrullah was a student of Hathazari madrasa.
It is now being investigated if the two suspects had links to any other attack though they told interrogators that this was their first mission.
The other detainee, Ariful Islam, is a student of Islamic law at Jamiul Ulum Madrasa in Mirpur. He had been missing since he took two days' leave about three months ago, said the madrasa principal, Delwar Hossain.
“I cannot recall when Airiful got admitted. It could be last year,” he said, adding police visited the madrasa to enquire about the student and took away some papers.
Meanwhile, the two were placed on an eight-day remand by a Dhaka court yesterday.
In the remand prayer, Mizanur Rahman, investigation officer of the Oyasiqur murder case, said the arrested youths confessed to the killing.
“We need to interrogate them to learn about others involved in the killing,” said Mizanur, officer-in-charge of Shilpanchal Police Station.
Following his appeal for a 10-day remand, the Dhaka Metropolitan Magistrate's Court passed the order.
Zikrullah told the court that they killed Oyasiqur and the main planner also took part in the attack but he managed to flee.
In a note with the remand prayer, the IO said the two suspects might have been involved in the Avijit murder though they had denied it.
During a briefing at the DMP media centre, Monirul Islam said they are looking into whether the duo had any link with the February 26 killing of writer-blogger Avijit Roy.
The DMP official said police have no assessment or intelligence regarding any previous threat to Oyasiqur, who often faced online backlash for his critical views about religion.
The arrestees know little about Facebook and blogs. Yet they killed Oyasiqur believing that it was their “pious duty”, he added.
Yesterday morning, Oyasiqur was buried in his family graveyard in Uttar Hajipur village in Ramganj upazila in Laxmipur after namaz-e-janaza at a village mosque. Earlier, his body reached the village around 3:45am.
His father, Tipu Sultan, said he has nothing to say regarding the arrest and trial of the killers. “I can't get back my son even if I spend crores or cut off one of my fingers,” he told The Daily Star over telephone.
Afsari Sultana, sister of Oyasiqur, said even if his brother made any mistake, nobody has the right to kill him.
She said many stay alive even after committing serious crimes. “Who are they to sentence my brother to death?” she said while talking to BBC Bangla Service last night.
The UN, the US, France and International Humanist and Ethical Union (IHEU) have condemned the brutal killing of Oyasiqur.