A close friend of Abdul Lathief Jameel Mohamed's said he became radicalised during his time in Australia.

The suicide bomber studied a postgraduate degree at Melbourne’s Swinburne University from 2009 before leaving the country in 2013.

"He was really angry with the US and its alliance’s attacks in Iraq during his stay in Australia," a close friend told Reuters.

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"He was really radicalized and became an extremist when he was in Australia. He returned as a completely changed person."

Sri Lanka’s prime minister Ranil Wickremesinghe said investigators have heard similar stories from family members.

"That’s how the family feel," Wickremesinghe told the Guardian. "We know there is some militancy going on in Australia among the Muslims. Australia has been out there fighting [in the war on terror]."

Attacker fails to hit his target

Abdul Latheef Mohamed Jameel, who was educated in Australia and Britain, was the only attacker out of the eight Sri Lankans pledging allegiance to Islamic State who failed to hit his intended target in the series of Easter Sunday attacks that killed at least 253, according to police.

His target was the breakfast buffet at the Taj Samudra, a luxury hotel on Colombo’s seafront. Instead, he ended up detonating his explosive device in a budget motel by the city’s zoo, killing a couple who had arrived only half an hour earlier.

People who knew him said Jameel, like many of the other bombers, was an educated family man who was radicalized after travelling abroad, though an attempt to reach Syria failed in 2014, according to a Sri Lankan intelligence source.

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The United States’ invasion of Iraq was a major turning point in Jameel’s views, people who knew him said.

An executive at the Taj familiar with some of the details of what happened on Easter Sunday, meanwhile, said Jameel most probably entered the hotel without being searched, but that his bomb failed to go off, in what the employee called a “miraculous escape” for its hundreds of guests.

After his failed attempt at the Taj, he checked in at the New Tropical Inn some 10 km (6 miles) away. He then left for several hours as a huge manhunt was being launched by authorities to catch those involved who were still alive, only to return later and detonate his device, according to the owner of the motel.

Privileged upbringing

Jameel, 37, was born in Kandy, the sixth child in a tea trading family of seven, according to interviews with three people who knew him well, all of whom declined to be named due to the ongoing police investigation. He was educated at the private Gampola International School in Kandy, a lush hilltown in the centre of the country.

The family’s relative wealth allowed him to travel and live abroad. He studied engineering at Kingston University, southwest of London, for a year in 2006, according to two sources close to the family and two European intelligence officials. The university declined to comment on his time there.

He returned to Sri Lanka, where he married and had his first of four children, before moving to Australia for four years in 2009. It was during this time he became radicalized, said those who knew him.

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Jameel attempted to travel to Syria in 2014 with a friend, but only got as far as Turkey before turning back for an unknown reason, according to the Sri Lankan intelligence source, who is familiar with Jameel’s travel during this time. The friend later joined Islamic State’s health service in Syria.

Returning to Sri Lanka again, he worked with his brother in the family tea business, but his relationship with relatives grew increasingly strained due to his religious views.

He was critical of secular education and once refused to allow his eldest son to attend a concert, saying that music was prohibited in Islam, according to one of his friends.

He later pulled his children from school, tutoring them at the family’s home in Wellampitiya, a suburb of Colombo. The house is near a copper factory owned by the family of two brothers who also detonated bombs on Sunday.

Read More Blood brothers: The wealthy family accused of orchestrating deadly Sri Lanka attacks

Investigators build a timeline of events

Jameel made little impression on the staff of the Taj when he entered some time before 8:45 a.m. on Easter Sunday. Waiters and chefs were preparing for the hotel’s popular brunch in the 116-seat Ports of Call restaurant.

There were no bag checks at the entrance, according to a Taj executive, who declined to be named due to the ongoing investigation.

“Since the end of the war, security has been more relaxed at all the hotels,” she said, referring to the 26-year conflict with Tamil separatists that ended in 2009. “We don’t know how long he was here for: he could have been here for some time. But it was miraculous escape for our guests.”

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Police have seized all copies of the hotel’s CCTV cameras to investigate what happened that day, she said.

As the coordinated blasts hit luxury hotels and churches, Colombo went into lockdown. But Jameel’s bomb failed to explode. He took an autorickshaw south to the New Tropical Inn where he checked in at 9:30 a.m., according to Sumith Wijela, the owner of the hotel.

Fifteen minutes later, he left without saying a word. It is not known where Jameel went during these hours, but around 1:30 p.m., he strolled back into the hotel, wearing a white shirt and carrying a bag, according to CCTV footage from a nearby house viewed by Reuters.

Minutes later, the building was almost levelled by a huge explosion.

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Wijela, who was watching TV in his office, down the corridor from Jameel’s room, was showered with plaster and concrete. Shrapnel pierced his right foot.

The blast blew a hole into the room next to Jameel’s, where a couple, the only guests at the time who had checked in less than 30 minutes earlier, were staying. Wijela pointed to a photo on his phone, showing the faded red bedspread where they were killed. He hadn’t even had a chance to learn their names, he said.

“I have been working for 20 years in this hotel, and all is finished in one day,” he said. “I have three daughters and there is nothing for them.”

At the Taj, meanwhile, Sunday’s events are also being felt. Soldiers patrol the ornate marble lobby in combat boots, and private security guards and hotel staff perform fingertip searches on the few guests checking in.

“Why didn’t you do this last Friday?” said the only other diner in the targeted restaurant to a waitress when Reuters visited on Friday, as the military searched the pool deck with hotel staff.