Before the blasts on Sunday, a memo warned of a potential attack and requested heightened security, a police source tells CNN.
The memo was dated April 11 and was signed by Sri Lanka's deputy inspector general of police.
Sri Lankan Minister of Telecommunication Harin Fernando tweeted a picture of the memo on Sunday.
"Some intelligence officers were aware of this incidence. Therefore there was a delay in action. What my father heard was also from an intelligence officer. Serious action need to be taken as to why this warning was ignored. I was in Badulla last night," he wrote.
CNN obtained a copy of the memo. Here's what it says:
April 11, 2019
Director/ Ministerial Security Division
Director/ Judicial security division
Director/ Retired presidents security Division
Acting Director/ Diplomatic security Division
Acting Director/ Retired presidents security Division
INFORMATION OF AN ALLEGED PLAN ATTACK
Reference to the letter of the defence ministry with regard to the above and the statement of IGP dated 2019.04.09 ref : STAFF05/IGP/PS/OUT/2860/19,
2. We would like to draw your special attention to the a page no 2 to 4 of the statement of the State Intelligence service stating that information has been received regarding an alleged plan of suicidal attack by the leader of ' Nations Thawahid Jaman ' Mohomad Saharan .
3. According to information of that statement ,would like you to give special attention and inform your staff to provide special security measures to the areas covered by your division.
Deputy Inspector General of Police