It is becoming ever clearer that the Sri Lankan Authorities knew that the attacks were going to happen... but did not do anything.
Sri Lankan police were warned repeatedly by Indian Intelligence services on the 4th and 20th of April before the attacks, including about the responsible organisation and its ringleaders.
Apparently however Sri Lankan Authorities did not pass the Information to the Government, possibly due to factionalism and political conflicts within the military/police itself and due to a lack of coordination and a power struggle between the President Sirisena and the Cabinet led by the Prime Minister Wickremesinghe (the former tried to fire the latter a couple of months ago).
And because of that 320+ people had to lose their lives, all of this entirely preventable.....
https://www.theguardian.com/world/2019/apr/23/pressure-builds-on-sri-lankan-officials-as-isis-claims-easter-attackshttps://edition.cnn.com/2019/04/23/asia/sri-lanka-investigation-ntj-intl/index.html
