After years of horrifying, deadly machete attacks in Bangladesh targeting dozens of secular bloggers, religious minorities, and activists of all sorts, investigators appear to have a clearer picture of who is perpetrating the attacks that have rattled the government and international observers. The break came after a pair of recent arrests led to one suspect fingering another as a coconspirator in a larger plot and, according to the New York Times, “touched off a cascade of revelations that, for the first time, has allowed the Bangladeshi authorities to penetrate the murky world of the attackers and answer questions about the planning, execution and purpose of the attacks…”

The attacks, which began in early 2013, have accelerated of late in the overwhelmingly Muslim country targeting Hindus and Christians. Just this week the wife of a police officer with a record of aggressively pursuing suspected militants was murdered. Monirul Islam, the new head of Bangladesh’s police counterterrorism unit, explained to the Times that investigators had learned there are two militant Islamic groups behind the attacks, Ansar al-Islam and Jama’atul Mujahedeen Bangladesh. Perhaps most importantly, Bangladeshi authorities told the Times “they now believe they have identified the top leadership of the two groups… and that they are preparing to round them up.”

Here’s more on how the deadly campaign of terror has been waged over the last three years:

… [The] militant Islamic groups [-] have gathered volunteers and recruits, trained them and eventually seeded them into cells run by a commander, Mr. Islam said. They have tried to pick their targets with care, with the aim of gaining support from the public, he said, and trained teams of killers. Their goal was to convert Bangladesh’s mixed secular and religious culture to an Islamist one, the chief investigator said… While the killers’ strikes often appear random, Mr. Islam says the terrorism campaign was conceived by the militant groups quite deliberately as a response to mass protests in early 2013, known collectively as the Shahbag movement. Inspired by a group of bloggers who led the protests, the demonstrators advocated an end to religion-based politics and the prosecution of war crimes dating to the 1971 war for independence… The Islamist groups appear to have reacted quickly to the Shahbag movement, mounting their first fatal attack on Feb. 15, 2013, against a blogger who wrote critically of Islam under the pseudonym Thaba Baba.

The Islamist groups’ tactics have been surprisingly effective in discrediting secularism and mobilizing popular opinion against it. “‘In general, people think they have done the right thing, that it’s not unjustifiable to kill the bloggers, gay people and other secularists,” the counterterrorism chief told the Times. “They have also put the secular government on the defensive. As a result, even as the government has condemned the killings, it has urged writers not to criticize Islam and warned that advocating ‘unnatural sex’ is a criminal offense.”