Police are looking at the possibility of a security lapse after which occurred after it emerged that one of the suicide bombers was earlier arrested, and later released.
Fresh reports have also indicated that the terrorists blew up a motorbike sometime back in the year test-run a grenade they had just assembled locally.
Members of the family of a Colombo spice trader have been arrested in connection to the Sunday blasts which claimed the lives of 359 people and injured another 500.
Two of Mohamed Ibrahim’s sons are suspected to have detonated the bombs in their backpacks in Shangri-La and another luxury hotel in Sri Lanka, an event that led to 39 foreigners’ deaths.
The island country with a general population of 22.4 million people was attacked with nine explosions in hotels and churches.
Major international intelligence departments are already in Colombo after the incident occurred.
Interpol, Scotland Yard and FBI are some of the investigators piecing together the terror links.
Wednesday, ISIS claimed responsibility for the attacks.
However, the Sri Lanka government believes the attacks must have been coordinated locally.
If found that that ISIS was involved in the attacks, this will be the highest death toll ever recorded from their attacks outside of Syria and Iraq.
Sri Lanka Prime Minister admitted that while the suicide bombers were on police radar for some time, they were well educated and from an affluent family, that it actually surprised authorities.
Prime Minister Ranil Wickremesinghe, said there was no compelling reasons to detain the Ibrahim brothers before the attack.
This happens against the backdrop of a major security lapse where police are said to have ignored red flags detailing even the names and photos of suspected terrorists.