In the days leading up to attacks on churches and hotels that killed 310 people on Easter, security agencies closely watched the little-known group that Sri Lankan officials now say carried out the strikes: National Thowheeth Jama’ath.

They had collected intelligence on the whereabouts of its leaders in an April security memo, which warned of Catholic church bombings. They had been warned even earlier by India that the group was plotting church attacks. And they knew as early as January that people potentially tied to the group were stockpiling weapons.

Officials said the organization most likely had help from an international network.

Why didn’t they act sooner? The government’s bitter infighting — between the president and prime minister — appears to have contributed to a security and communication breakdown. So far, there are no complete answers to why more was not done to thwart the bombers.