COLOMBO, Sri Lanka — The confidential security memo laid it all out: names, addresses, phone numbers, even the times in the middle of the night that one suspect would visit his wife.
In the days leading up to the devastating suicide bombings that killed at least 310 people in Sri Lanka on Easter Sunday, the country’s security agencies had been closely watching a secretive cell of the National Thowheeth Jama’ath, a little-known radical Islamist organization that security officials in Sri Lanka now say carried out the attacks and may have received help from abroad.
They knew the group was dangerous. They had collected intelligence on the whereabouts of its leaders in the April 11 security memo, which warned of Catholic church bombings. They had been warned even earlier by India that the group, also known by the spelling National Thowheed Jama’ath, was plotting church attacks. They knew as far back as January that radical Islamists possibly tied to the group had stockpiled weapons and detonators.
And within hours of when three churches and three hotels were bombed, Sri Lankan security services swooped down on at least 24 suspects, suggesting that they also knew exactly where the group had been operating.
Why the security agencies failed to act aggressively on the information before the bombings is now an enormous question. It has been further complicated by a feud between the president and prime minister, which left the prime minister ignorant of the information the security agencies possessed — leading to bitter recriminations that have created a new government crisis.
The history of bitter infighting between Sri Lanka’s leaders appears to have contributed to a spectacular security breakdown that led to one of the world’s deadliest terrorist attacks.
One of the suicide bombers had even been arrested just a few months ago, Sri Lankan officials disclosed on Monday, on suspicion of having vandalized a statue of Buddha, an inflammatory act in a Buddhist-majority nation where strident religiosity, on all sides, seems to be increasing.
On Monday, several ministers lashed out at President Maithripala Sirisena, who controls the security services, for not acting on the detailed warnings before the attacks.
“We are ashamed of what has happened,” said Rauff Hakeem, the minister of city planning. “If the names of the persons involved were already known, why were they not arrested?”
He called the attacks a “colossal failure on the part of the intelligence services.”
Several ministers are now calling for the national police chief to resign. Others questioned how such a homegrown group could have acted alone.
“There was an international network without which these attacks could not have succeeded,” said Rajitha Senaratne, the health minister.
Sri Lanka’s president has not provided any satisfying answers about why the security services did not do more to thwart the bombers. Shiral Lakthilaka, a senior adviser, denied that there had been any security lapses. “Everyone has done their job,” he said. “These kinds of alerts are coming time to time. Even U.S. or anyone will not try to panic people.”
But he said that the president had appointed a special committee, led by a Supreme Court judge, to investigate the matter. And he acknowledged that the warnings about National Thowheeth Jama’ath — disclosed in the April 11 memo from a top police official to division heads — had been circulated only among police officials in charge of “VIP security.”
[Read a translated summary of the memo.]
“That is why the president has appointed the committee to understand and ascertain what went wrong,” Mr. Lakthilaka said.
The warnings appear to have gone back even further.
India, a close ally of Sri Lanka’s, has been watching the entire South Asia region for any sign of activity by Al Qaeda or the Islamic State. And Indian security agencies had been scrutinizing the movements of National Thowheeth Jama’ath’s leader, Mohammed Zaharan, a known extremist who has spent time in both India and Sri Lanka, and who in recent years has preached hateful messages online.
As early as April 4, the Indians provided the Sri Lankans with cellphone numbers and information about Mr. Zaharan and his lieutenants who they said were planning suicide attacks on Catholic churches and the Indian Embassy in Sri Lanka, several Sri Lankan and Indian officials said.
The Sri Lankan security services then ran down addresses and put several members of the group under close surveillance.
The April 11 memo included precise information, such as the observation that Mr. Zaharan’s brother, an avid recruiter for the group, “visits his wife and children in the nights (2300hrs -0400hrs)” and it listed an exact address, down to a house number and cross street.
But with Sri Lanka’s president and prime minister feuding for months, leading to a political breakdown last year, it seems that the president excluded the prime minister from top security briefings and that the prime minister’s office had no inkling of the warnings of imminent suicide attacks.
Whether sharing that information would have made a difference is unclear. But the prime minister and his allies are claiming that had they known, they would have insisted on more security at the targeted sites.
On Monday, the country remained on edge. At a crowded bus station in the capital, Colombo, police officers found 87 bomb detonators.
As mourners hung white flags around their houses and prepared to bury their dead, Mr. Sirisena declared a conditional state of emergency that gave the security services sweeping powers to arrest, interrogate, search and seize.
A dusk-to-dawn curfew remained in effect. Schools were closed. So were many shops. Traffic on the main roads remained light, and tourists who visit this tropical island at this time of year were canceling hotel bookings.
The National Thowheeth Jama’ath group emerged around 2015 in the aftermath of attacks against Muslims. Though Sri Lanka has been mostly spared the religious-driven bloodshed of other South Asian nations, such as India and Pakistan, in recent years some Buddhist monks have become militant and incited followers to attack Muslims. The Sri Lankan government’s security services appeared to have turned a blind eye, letting Buddhist mobs act with impunity.
In 2014, scores of people were injured and three were killed in Buddhist-Muslim clashes. Some Muslims then joined radical Islamist groups that they believed would defend their faith. Still, few Sri Lankans said they had ever worried about the possibility of the country’s religious minorities attacking one another. Muslims make up about 10 percent of the population and Christians 7 percent, compared with Buddhists at 70 percent.
According to the April 11 security memo, National Thowheeth Jama’ath’s leader, Mr. Zaharan, had been under close watch for several days. Sri Lankan security officials have blamed his group or allied groups for vandalizing Buddhist statues in December, seen as an attempt to instigate bloodshed between Buddhists and Muslims.
But in January, Sri Lankan officials said that evidence had emerged that homegrown Islamist groups were even more dangerous. Investigations connected to the statue destruction led police officials to a remote coconut plantation in northwestern Sri Lanka where officers discovered an elaborate weapons cache with more than 100 kilograms of explosives, detonators, wire cords, a rifle, bullets, dry rations and religious propaganda.
Sri Lankan officials have since said that the cache belonged to a radical Islamist group, probably connected to National Thowheeth Jama’ath. But several security specialists said that even if true, it was unlikely that National Thowheeth Jama’ath members could have carried out the Easter bombings on their own.
The group had never attempted such a devastating, coordinated attack, with numerous suicide bombers striking different places nearly simultaneously. Some of the bombs were extraordinarily powerful. The explosion at a church in Negombo, north of Colombo, blew off much of the high vaulted roof. Clay ceiling tiles rained down, and dozens of people died.
Experts said the choice of Christians as a target might mean that a more international extremist group with a broader anti-Christian agenda was involved.
“There’s no reason for local extremist groups to attack churches, and little reason to attack tourists,” said Amarnath Amarasingam, a specialist in Sri Lankan extremism at the Institute for Strategic Dialogue, a counterterrorism research group in London. “The target selection and attack type make me very skeptical that this was carried out by a local group without any outside involvement.’’
No warning seemed to have been communicated to any target. Managers and employees of some of the fanciest hotels in Colombo said they had not received any alert. That included the waterfront Galle Face Hotel, which is next door to the Indian High Commission and is frequently visited by senior officials and foreign dignitaries.
“No one told us anything,” said Shafraz Nawaz, who works at the Galle Face. “It was normal operation. But security has increased after the attack now.’’
Sri Lankan officials said they did not know Mr. Zaharan’s whereabouts on Monday. Indian intelligence officials suggested that he might be hiding in eastern Sri Lanka.
In Washington, intelligence and counterterrorism analysts were scrutinizing possible ties between the Islamic State and the attackers, but as of Monday afternoon had not yet reached any definitive conclusions.
Nicholas J. Rasmussen, a former director of the National Counterterrorism Center, said that the presence of some Sri Lankan fighters in Syria and Iraq raised the prospect of informal connections with members of National Thowheeth Jama’ath.
“It’s hard to imagine an attack of this complexity without some form of organization and support from a group that has done this kind of thing before,” he said in an email.
Lisa Monaco, who served as Homeland Security adviser for President Barack Obama, said that if the attacks in Sri Lanka were inspired by the Islamic State, they should serve as a stark reminder to the Trump administration.
“We should not mistake the defeat of the physical caliphate with that of the virtual caliphate,” Ms. Monaco said.
“It’s a movement,” she said. “And it, as we’ve seen, can take hold around the world.”