Several wealthy and middle class people with international connections believed to be behind the attacks in Sri Lanka.
One of the ringleaders of the Sri Lankan terror attacks was believed to be the son of a wealthy spice tycoon who was “brainwashed” by his radical younger brother, according to local media.
The suicide attacks on Easter Sunday killed more than 359 people and injured about 500 others, targeting three churches and four luxury hotels.
Thirty-three-year-old copper factory owner Inshaf Ibrahim detonated his explosive device at the busy breakfast buffet of the luxury Cinnamon Grand hotel restaurant, a source close to the family said.
His 31-year-old brother Ilham Ibrahim is also dead - although there are conflicting reports he either blew himself up using a suicide vest at the Shangri-La hotel, or when later confronted by police at his home.
Police raided the younger brother's home, following the coordinated attacks, where a bomb exploded, killing Ilham's pregnant wife and the couple's three children.
The ABC is reporting that his wife, Fatima, was the one responsible for triggering the explosive device.
The brothers' names were reported in local media, but Sri Lankan authorities have not released the identities of any of the bombers, and police did not respond to request for comment.
Police said the brother's father, understood to be Mohamed Ibrahim, was arrested as part of the investigations.
Ibrahim, a wealthy spice trader and pillar of the business community, had six sons and three daughters before the attacks.
"He was famous in the area for helping the poor with food and money. It's unthinkable his children could have done that," neighbour Fathima Fazla said.
"Because of what they have done, all Muslims are treated as suspects."
Known radical connections
Ilham Ibrahim openly expressed extremist ideologies and had been involved in meetings of National Thowheed Jamath, a local Islamist group suspected of involvement in planning the attacks, according to the source close to the family.
His entrepreneur brother, Inshaf, was outwardly more moderate in his views, and was known to be generous with donations to his staff and struggling local households.
Inshaf was married to a daughter of a wealthy jewellery manufacturer and had no problems with money.
"I was shocked. We never thought they were these kind of people," said Sanjeewa Jayasinghe, a 38-year-old network cabling engineer who works next door to the Ibrahim family home.
Authorities confirmed another suicide bomber had previously studied in the UK and in Australia.
Sources have named him as Abdul Lathief Jameel Mohammed.
Cleric also behind the attacks
Sri Lanka's government has also accused cleric Zahran Hashim indirectly for the attacks, saying the Islamist group he was believed to lead, the National Thowheeth Jama'ath, carried out the bombings.
For years, Sri Lanka's Muslim community warned authorities about the firebrand cleric.
A video released by the Islamic State group after it claimed responsibility for bombs that killed 359 people, appears to prominently feature Hashim.
The round-faced cleric is the only one of the eight figures whose face is uncovered.
Hashim had attracted several thousand followers on social media sites, including YouTube and Facebook, where he posted incendiary sermons.
The vice-president of the Muslim Council of Sri Lanka Hilmy Ahamed said he had gone to local authorities with concerns about Hashim three years ago.
"This person was a loner and he had radicalised young people in the guise of conducting Koran classes," he said.
"But nobody thought these people were capable of carrying out an attack of such magnitude."
Sri Lankan officials are still investigating to what degree IS may have helped the attackers, but Mr Ahamed said Hashim was known to have international ties.
"All his videos have been uploaded from India. He uses boats of smugglers to travel back and forth from southern India," he said, "I don't know if he is dead or alive."
Police are carrying out DNA tests on the bodies of some of the bombers.
"The biggest concern is Zahran," said an officer close to the investigation.
"Anyone who can help us trace him will be doing everyone a huge favour," the official added. "We have not been able to account for him yet."
Some of the bombers are still believed to be at large.
With Reuters and AFP