For many Sri Lankans, it was a horrific shock to learn that local Muslims could have been behind the suicide attacks that killed more than 250 people last month. How could a small group have planned such a devastating wave of bombings undetected? The clues were there in mid-January, when Sri Lankan police stumbled upon 100kg (220lb) of explosives and 100 detonators, hidden in a coconut grove near the Wilpattu national park, which is a remote wilderness in Puttalam district on the west coast of the country. Police were investigating attacks on statues of the Buddha by suspected Islamist radicals elsewhere in the country. Four men from a newly formed "radical Muslim group" were arrested. Three months later, suspected Islamists blew themselves up in packed churches and hotels in Colombo, Negombo and the eastern city of Batticaloa killing more than 250 people, including 40 foreigners. But that arms seizure in the coconut grove was not an isolated incident. It was just one of several suspicious incidents in the months leading up to the bombings that should have rung alarm bells, especially given reports that several Sri Lankans who had joined the Islamic State group in Syria were back home. It didn't. We now know the carnage on Easter Sunday happened despite repeated warnings about potential attacks from intelligence services in neighbouring India and the US. It was only after the bombing that police identified links between two of those arrested in Puttalam in January and the suspected ringleader of the mass-casualty attacks. Family circlesPolitical in-fighting and factionalism going all the way to the top of the Sri Lankan government is part of the reason warnings went unheeded, but complacency about the peace in Sri Lanka since the end of the civil war in 2009 also played a role. Sporadic anti-Muslim riots since the end of the war between Tamil minority separatists and the government had fomented anger and discontent, but on the face of it nothing had pointed to a co-ordinated assault of this magnitude. "The Islamists surprised everyone with the deadly bombings and at the same time kept the entire operation a secret," said a former Sri Lankan counter-terrorism operative who had been keeping a tab on some of the radicals involved in the Easter Sunday attacks. It would have required detailed planning, safe houses, an extensive network of planners and handlers, expertise on bomb-making and significant funding - so how did all of this slip so far under the radar? Few of these questions have been answered, but sources linked to security agencies, government officials and local Muslim leaders have painted a picture of how, over the years, a small number of die-hard radicals and IS sympathisers clandestinely set up cells right under the noses of the security forces. Investigators say that certain members of individual families became radicalised and operated as units. "That's how they kept their intentions and movements among themselves," said the counter-terror agent, who requested anonymity to speak openly, given the sensitivity of ongoing investigations. Each unit then liaised with other radicalised family groups, forming larger networks. The supposition goes that information was tightly protected within networks of loyalty that transcended ideology. Encrypted social media networks and messaging apps are believed to have facilitated communication and planning. "The investigators are now trying to find out how these people communicated and co-ordinated," the agent added. "Using families to achieve their aim seems to be part of a new trend among these radicals. We have seen how some families were involved in suicide attacks [on a church and a police building] in Indonesia last year," said the former agent. So far more than 70 people believed to be linked to the radicals have been arrested. But not everyone is convinced the networks have been dismantled. "The main people involved in the attacks and those who made these bombs are still at large… So there are suggestions that there may be a second wave of attacks," a senior government official who did not wish to be identified told me last week. "According to the theory of conventional terrorism, every suicide bomber needs at least five handlers. If you go by that there are 45 guys [for nine bombers] still out there. We are concerned." It's a narrative at odds with what Prime Minister Ranil Wickremesinghe has been saying. He recently declared that all suspects connected with the bombings had either been apprehended or killed. The bombings have now put the spotlight on Muslims - the third biggest community in Sri Lanka, after the majority Sinhalese and Tamils. Muslims constitute around 10% of the country's population of 22 million. AFP.