Highly educated and financially independent -- that's how Sri Lanka's deputy defense minister described many of the suicide bombers who killed hundreds of people in a wave of coordinated attacks across the island nation on Sunday.
"They're quite well-educated people," Wijewardene said at a press conference Wednesday in Colombo, the country's capital.
According to Wijewardene, the suicide bombers had splintered away from a little-known local extremist Muslim group, National Towheed Jamaar, and another group which he identified only as "JMI." The former was earlier blamed for the deadly blasts by Sri Lanka's health minister.
“Their thinking is that Islam can be the only religion in this country," Wijewardene told reporters.
At least 359 people were killed and another 500 were injured Sunday when near-simultaneous explosions took place at eight locations across Sri Lanka, a largely Buddhist country located off the southern tip of India. Most of the explosions were detonated by suicide bombers, according to Wijewardene.
Thirty-nine foreigners were among the dead, Wijewardene said. That includes at least four Americans, according to a U.S. official briefed on the investigation.
At least 46 children were also among those killed, with the youngest being just 18 months old, according to the United Nations Children's Fund, which cited the Sri Lankan government.
Intelligence services believe the bombings were motivated by last month's attacks on two mosques in New Zealand that killed 50 people, according to Wijewardene, who wouldn't elaborate further but said there was "a major lapse in sharing information" prior to the Easter blasts.
Explosions erupted at three churches holding Easter services in Colombo, Batticaloa and Negombo. Blasts also tore through three hotels in Colombo, including some that are upscale and popular among Western tourists, according to Sri Lankan police.
Hours after the initial bombings, another explosion rang out at a housing complex in Dematagoda, a suburb on the outskirts of Colombo, police said.
Later that night, the Sri Lankan Air Force initiated a controlled explosion of a 6-foot-long pipe bomb that was detected on a road near Colombo International Airport, according to Sri Lanka Air Force spokesman Gihan Seneviratne.
A fourth hotel was targeted in a failed attack that day, according to Sri Lankan Prime Minister Ranil Wickremesinghe.
The group's ringleader detonated his explosive-laden vest at the Shangri-La Hotel in Colombo, according to Wijewardene.
The female suicide bomber detonated inside the housing complex in Dematagoda as authorities approached, killing two children and three police officers. She was the wife of another alleged assailant, who is among the 60 people arrested so far in connection to Sunday's deadly attacks, a junior spokesman for the Sri Lankan police told ABC News.
Sri Lankan police also told ABC News that a man arrested in a house raid in January was among the suicide bombers.
And according to a Sri Lankan police source, two of the suicide bombers have been identified as sons of a Sri Lankan businessman and spice trader, who is being held by authorities along with four of his other sons.
All 60 of those arrested are Sri Lankans and 32 of them are in custody with Sri Lanka's Criminal Investigation Department. Authorities have conducted raids across Sri Lanka in the wake of the blasts, locating at least two safe houses, according to Wijewardene, who warned the public to remain vigilant as authorities track down any other possible suspects.
The Islamic State group has claimed responsibility for the series of explosions in Sri Lanka, releasing an image through its Amaq news agency on Tuesday that it said shows the attackers' leader in front of an ISIS flag standing alongside seven others with their faces covered by black-and-white headscarves. The terrorist organization offered no other evidence to support its claim.
Sri Lanka's prime minister acknowledged the claim during a press conference Tuesday but appeared to be unsure of ISIS's involvement.
"All that we knew earlier is that there were foreign links and that this could not have been done just locally," Wickremesinghe told reporters. "There has been training done and a coordination which we [have] not seen earlier."
The United States sent a team of FBI agents and military officials to help Sri Lankan authorities with the ongoing investigation. Intelligence units from Australia, India, the United Arab Emirates, the United Kingdom and the International Criminal Police Organization are also assisting.
The U.S. Embassy in Colombo and all American spaces in Sri Lanka will remain closed to the public through Friday.
ABC News' Alexandra Faul, Ben Gittleson, Angus Hines, Josh Margolin, Elizabeth McLaughlin, James Meek, Kirit Radia, Nadine Shubailat and Alex Stone contributed to this report.