COLOMBO, Sri Lanka—On April 9, Sri Lanka’s intelligence services warned the island nation’s police about Zahran Hashim, a local Muslim who preached hard-line Islamist views, saying he and his associates were planning to carry out a terrorist attack. The alert said the group was targeting churches and had already scouted locations.
Then, Sunday, suicide bombers struck three Christian houses of worship and three luxury hotels, leaving more than 250 people dead.
Mr. Hashim, who had gained notoriety for fiery online sermons, promoted the idea of a Muslim caliphate and questioned democracy as a form of government, two intelligence officials said.
Police say a group founded by Mr. Hashim, or at least some of its members, played a role in the Easter attacks. In a video released by Islamic State on Monday claiming responsibility, Mr. Hashim appears to be the one plotter whose face is exposed as he leads seven others swearing loyalty to Islamic State, according to people who have known him.
Sri Lanka’s health ministry said Thursday that the bombings killed 253 people, revising the toll from 359 dead because of difficulties identifying and counting so many mutilated victims.
Intelligence officials said Mr. Hashim founded his group, National Thowheeth Jamath, which translates to National Unification Group, in 2012, and was its leader, at least until recently.
The preacher and his followers were radicalized in the aftermath of a brutal civil war between the government of the Buddhist-majority country and Tamil-speaking separatists, in which Sri Lankan’s minority Muslim community was often targeted, according to a Muslim community leader who knew Mr. Hashim as a young man.
Sri Lankan authorities said they have identified eight of nine Sri Lankan suicide bombers who took part in the attacks. President Maithripala Sirisena told reporters on Friday that Mr. Hashim is believed to be one of the attackers who blew himself up at the Shangri-La hotel.
One of the intelligence officials said authorities are awaiting DNA test results to determine if Mr. Hashim was one of the bombers.
Sri Lankan agencies were aware of Mr. Hashim’s online video sermons on Islam for many years, the two intelligence officials said. Since December, his name popped up repeatedly on the radar of security and intelligence agencies in connection with issues including the defacement of Buddhist statues and recruitment for Islamic State, they said.
Mr. Hashim spent years waging ideological battles, often against fellow Muslims who disagreed with his hard-line views, said people who knew him and followed his activities.
He embraced a puritan form of Islam known as Salafism, and rejected the less strict traditional schools of Islam followed by the local Tamil-speaking community, according to two members of the Muslim community who knew him. He rejected the traditional practice of venerating saints as a transgression of Islam’s tenet that there is only one god.
Mr. Hashim grew up in the eastern coastal city of Kattankudy, a community in Sri Lanka that is predominantly Muslim. Muslims make up about 10% of the island’s population, which is dominated by Sinhalese-speaking Buddhists, who make up 70% of the population.
In 1990, when Mr. Hashim was growing up, more than 100 Muslim worshipers were gunned down at mosques in or near his hometown. The government blamed the attack on the separatists.
“His approach was very intolerant and violent,” said a Muslim community leader who tried to stage an intervention when Mr. Hashim was young. “We saw it as an issue, but we also clearly saw his potential and that’s why we told him to be mindful of his approach.”
Mr. Hashim didn’t change his approach, however, and he was ultimately expelled from his madrassa in his 20s without graduating, the community leader said.
Mr. Hashim stayed in Kattankudy and established a group to study the Quran and to inculcate young people into his fundamentalist version of Islam, according to Hilmy Ahamed, vice president of the Muslim Council of Sri Lanka, who became aware of Mr. Hashim’s activities after community members complained to him.
“He basically started brainwashing,” instructing students that Buddhist statues were idols that must be defaced, Mr. Ahamed said.
Mr. Ahamed said his organization began repeatedly warning authorities about Mr. Hashim’s radicalism in 2015.
In the months leading to the attack, Mr. Ahamed sent Mr. Hashim’s sermons to an intelligence officer, he said. The officer responded, “Noted. Thanks,” he said.
Mr. Ahamed said, however, that he was surprised that Mr. Hashim had become a notorious figure accused of plotting major violent attacks. “We just thought he was a loner uploading videos on YouTube and other social media,” he said.
Behind the scenes, intelligence agencies were noticing the videos growing more radical, the two intelligence officials said. Mr. Hashim railed against non-Muslims and exhorted young people to grab territory from other ethnic and religious groups for Muslims, they said. Still, authorities said his activities remained within legal bounds, the officials said.
But in March 2017, police moved to arrest Mr. Hashim after he was accused of assaulting members of a more moderate Muslim group in Kattankudy, the intelligence officials said. Police issued a warrant for his arrest and Mr. Hashim went into hiding. Other members of his group also fled, according to a security memo seen by The Wall Street Journal.
For the next 20 months, information gathered by Sri Lankan intelligence agencies suggested that Mr. Hashim traveled around the country and may have taken a boat to India before returning to Sri Lanka.
He was back on their radar in December, when a group of people defaced Buddhist statues in the town of Mawanella, east of the capital. The April 11 security memo said Mr. Hashim was involved.
A month before the attack, intelligence officials received information that Mr. Hashim had been recruiting for Islamic State, the intelligence officials said. Not long after, intelligence gathered by India and Sri Lanka’s own security agencies concluded an attack was coming.
“We should have connected the dots long before,” one of the officials said. “But no one thought he could do something like this.”
Write to Jon Emont at jonathan.emont@wsj.com and Niharika Mandhana at niharika.mandhana@wsj.com
