- Al Qaeda, ISIS have claimed responsibility for murder of activists
- ISIS, Al Qaeda not active in Bangladesh, assailants home grown: Police
- In one case, killers admit influence of cleric trained in Hyderabad
Within hours, in keeping with a pattern of the past year, a spokesperson for Al Qaeda in the Indian Subcontinent or AQIS sent out a tweet claiming credit for the murder.
It is the latest chapter in what - according to one theory - appears to be deadly competition between Al Qaeda and its even more violent offspring, ISIS, to establish dominance over Bangladesh's jihadist landscape.
In the past two months alone, there have been four such killings: in end February, ISIS claimed credit for the murder of a Hindu priest in northern Bangladesh. In the first week of April, Al Qaeda claimed credit for killing of a secular student activist. Two weeks later, ISIS claimed they were behind killing of an English professor in Rajashahi, a university town north of Dhaka.
And then came the killing of Mr Mannan, claimed by Al Quaeda.
David Bergman, a Dhaka-based freelance journalist told NDTV that "it doesn't mean that ISIS or Al Qaeda are operational in Bangladesh, or that they have a base here. But they have some ways of communicating here. It is pretty clear even as the government is denying it. "
"There is no IS, there is no Al Qaeda in Bangladesh, these criminals are home grown criminals," said AKM Shohidul Haq, Bangladesh's Inspector General of Police, in response to a question from NDTV.
Under pressure to produce results, the Bangladesh police released fresh data, showing that for the 37 acts of Jihadist violence over the past year, they have made 144 arrests.
A majority of the acts - especially the murders of secular bloggers - are attributed to what the police call local outfits: Ansarullah Bangla Team, a newly formed militant outfit or the older Jamiat ul Mujahideen Bangladesh or JMB.
But, the core of this claim remains controversial -- it revolves around confessions, of which the police have extracted 49 in all.
NDTV accessed the confessional statements of the killers of Rajeeb Haider, the first blogger to be killed in February 2013, a case which serves as a template for the multiple investigations under way.
Four young men, said to be members of Ansarullah have been convicted for the crime. All of them are students at Dhaka's North-South University.
All four say they were angered by writings of bloggers which supposedly denigrated Islam, but that they were incited to violence by the speeches of a firebrand cleric, Jasimuddin Rahmani.
Rahmani, until the arrests, had remained relatively unknown, but police say he is the mastermind of Ansarullah. In his confession, he says he received training in Abusallam madrassa in Hyderabad in India for two years and eventually went on to become a preacher in Markazul Uloom Al Islamiya mosque in Dhaka.
In 2010, he began to speak out against atheists and authored a book titled Open Sword which police insist has acted as a touchstone for jihadists.
But, the lawyers for these men contest these claims. Advocate Farrukh Ahmed, who represents many of them, says, "The police are taking these confessional statements forcefully, they are taking the accused in police remand and torturing them mentally and physically. I told the High Court that this is absolutely not the way to get it."
Benazir Ahmed, the DIG of the Rapid Action Batallion or RAB -- Bangladesh's counterterrorism force -- told NDTV, "We do not just depend on confessions, we investigate. In my law, the confession should be substantiated with other evidence, forensics and everything."
Mr Ahmed, however, said that the police investigations are starting to unravel. Out of the 33 men accused in the 6 cases he represents, 11 have got bail.
Global jihadist turf war or local militancy - either way the unending body count shows Bangladesh's attempts to check the violence remain open to question, a turmoil unfolding not far from India's borders.