Two experts offer their insight, one via 'The New Yorker' magazine and they explain:
To discuss Sunday’s atrocities and the political situation in Sri Lanka, I spoke by phone with Amarnath Amarasingam, a senior research fellow at the Institute for Strategic Dialogue who studies extremism in Sri Lanka and the region. During our conversation, which has been edited for length and clarity, we discussed social media’s role in exacerbating ethnic conflict, concerns about Islamic extremist groups gaining a foothold in Sri Lanka, and the Buddhist majority’s “majority within the minority” complex.
Link:https://www.newyorker.com/news/q-and...pes-sri-lanka?

His bio:https://www.isdglobal.org/isd_team/amarnath-amrasingam/

Then there is Jason Burke, in 'The Observer' who adds context and some insight. A far degree of government chaos is apparent, although it appears the police quickly knew where to go - at some cost sadly.
Link:https://www.theguardian.com/world/2019/apr/22/sri-lanka-bombings-islamist-group-blamed-but-focus-also-on-failure-of-security-forces?