Two hundred and fifty-three people were killed in the devastating Easter weekend blasts, and more than 500 were injured.
Now the US ambassador to Sri Lanka has made a dire warning in the wake of the slaughter.
Alaina Teplitz told Reuters: “We do believe that the terrorist threat is ongoing and there may be active plotters.
“Active members of the attack group that carried out the terror attacks on Easter Sunday may still be at large.
“We certainly have reason to believe that the active attack group has not been fully rendered inactive.
“We do believe that there is active planning under way.”
Sri Lanka’s government has blamed a domestic Islamist extremist group – the National Towhead Jamaath (NTJ) – for carrying out the bombings.
But authorities also believe it would have required help from international terror networks to carry out such a co-ordinated and devastating attack.
Sri Lanka’s Prime Minister Ranil Wickremesinghe last week said ISIS may be linked to the blasts.
He told reporters: “This could not just have been done locally.
“There had been training given and a co-ordination which we are not seeing earlier.”
ISIS earlier claimed responsibility and identified seven terrorists allegedly responsible for the atrocities.