ITV News has obtained CCTV footage which shows the Sri Lanka suicide bomber, who studied in the UK and Australia, walking into a guesthouse moments before he blew himself up, killing two people.
The footage, captured on a neighbour's CCTV, shows a man - who sources have named as Abdul Lathief Jameel Mohamed - wearing white and a backpack.
He disappears from the camera's view as he enters the Tropical Inn guest house in Dehiwala, a suburb of Sri Lanka's capital Colombo, where he went on to detonate his explosives.
The images have been released as the UK Foreign Office has advised against all but essential travel to Sri Lanka.
Sri Lanka's Prime Minister Ranil Wickremesinghe has warned suspects linked to the Easter Sunday bombings are still at large and could still have explosives.
Images of three men and two women who are being hunted by police have been released.
The death toll has also been revised down from 359 to 253 due to a calculation error said the Sri Lankan health ministry on Thursday evening.
Mohamed's sister Samsul Hidaya has revealed her brother was radicalised during his studies abroad. Upon his return to Sri Lanka she said he was ''angry and totally crazy'' in his manner, often criticising his family for not being religious enough.
ITV Asia Correspondent Debi Edward said Mohamed had retreated to the guesthouse after his bomb had failed to detonate in the breakfast room of The Taj hotel in Colombo.
The CCTV footage shows him pacing around the streets outside the Tropical Inn.
Ms Edward said: ''That is where we believe he then tried to repair his suicide vest and in the process he accidentally detonated it, killing himself and two innocent guests at that guesthouse.
''It is thought he might have retreated to that area on the outskirts because it is close to the zoo here in Columbo which would have been busy on Easter Sunday and is also close to a catholic congregation of more than 1,000 people.''
Police are continuing to hunt for explosives and more people behind the bombings. Ms Edward said: ''Tonight they have confirmed they are searching for three men and women who are still on the run.''
In addition to the 253 people who died, more than 500 were wounded in the Easter Sunday attacks.
Sri Lanka's catholic churches have suspended all public services over security fears and Muslims have been urged to avoid gathering for Friday prayers.
Sri Lankan Defence Secretary Hemasiri Fernando has also resigned, taking responsibility for the terror attacks.
Mohamed is believed to have studied in south-east England in the early 2000s, before going on to study in Australia and then returning to Sri Lanka.
Speaking to MailOnline, Mrs Hidaya said: ''My brother became deeply, deeply religious while he was in Australia. ''He was normal when he went to study in Britain, and normal when he came back. ''But after he did his postgraduate in Australia, he came back to Sri Lanka a different man. ''He had a long beard and had lost his sense of humour. He became serious and withdrawn and would not even smile at anyone he didn't know, let alone laugh.''
Mrs Hidaya described her brother as devout when he was a child and added that when he returned from Australia he became more critical of his family and ''created tension'' by berating his family for what he thought were religious lapses, she told the website.
The father of two of the suspected Easter suicide bombers has been arrested on suspicion of aiding his sons, according to Sri Lanka’s former navy chief, Jayanath Colombage.
Six near-simultaneous explosions took place shortly before 9am local time in the morning - three at churches and three at luxury hotels.
In Colombo, St Anthony's Shrine and three luxury hotels - the Cinnamon Grand, Shangri-La and Kingsbury, were targeted.
Other blasts were reported at St Sebastian's Church in Negombo, a majority Catholic town north of Colombo, and at Zion Church in the eastern town of Batticaloa.
A few hours later, two more blasts occurred just outside of Colombo, one of them at the guest house, where two people were killed, the other near an overpass.
Three police officers were killed during a search at a suspected safe house on the outskirts of Colombo when its occupants apparently detonated explosives to prevent arrest.
Despite so-called Islamic State claiming responsibility for the attacks and releasing images that purport to show the bombers, Sri Lankan authorities say they have not yet determined whether the atrocities were directed or inspired by the terror group.
Sri Lankan authorities have blamed a local extremist group, National Towheed Jamaar (NTJ) - who previously had only defaced Buddhist statues - for the attack, but they have not claimed responsibility.
Speaking on Wednesday, Sri Lanka's Defence Minister Ruwan Wijewardenesaid said the bombers' association with so-called IS was “through ideology, maybe funding”.
On Wednesday, Sri Lankan Prime Minister Ranil Wickremesinghe has said the Government had evidence that the bombings were carried out “by an Islamic fundamentalist group” in retaliation for the March 15 mosque shootings in New Zealand, that killed 50 people, although he did not disclose what the evidence was.
Also speaking on Wednesday, Sri Lanka's Defence Minister Ruwan Wijewardene said “weakness” within Sri Lanka’s security apparatus led to the failure to prevent the nine bombings.
Neither the President, Prime Minister or his Cabinet are said to have been informed of information suggesting attacks were planned, exposing continuing turmoil in Sri Lanka’s government.
“By now it has been established that the intelligence units were aware of this attack and a group of responsible people were informed about the impending attack,” Mr Wijewardene said.
“However, this information has been circulated among only a few officials.”
Prime Minister Wickremesinghe called for the resignations of the country's defence secretary and national police chief in response to the claims.
In a live address to the nation Sri Lanka’s president, Maithripala Sirisena, said he also was kept in the dark on the intelligence about the planned attacks.
Mr Sirisena vowed to “take stern action” against the officials who failed to share the information and also pledged “a complete restructuring” of the security forces.
A mother and her two children, a brother and sister, a married couple, and a businesswoman from Manchester were the eight British victims killed in the attacks.
Anita Nicholson, her son Alex, 14, and daughter Annabel, 11, who died when one of seven suicide bombers struck as they ate breakfast at the Shangri-La hotel in Colombo.
Londoner Matthew Linsey’s daughter Amelie, 15, and son Daniel, 19, were killed in the same blast on the final day of their holiday.
GP Sally Bradley and her husband Bill Harrop, a retired firefighter, from Manchester, died in the Cinnamon Grand Hotel bombing.
The eighth victim is Lorraine Campbell, 55, from Manchester, who was staying at the Cinnamon Grand Hotel on a business trip.