Sunday.

Most of them occurred within a single half-hour.

The targets were churches and popular hotel restaurants.

Nearly 300 people were killed.

Afterwards, three bombs detonate

as police look for suspects.

Sri Lankan officials have blamed

a little known radical Islamist group

for the violence.

Here's how the Easter Sunday attacks unfolded.

What they show is a level of sophistication

and coordination that resulted in one of the deadliest

terror attacks in modern history.

The story actually begins 10 days earlier, on April 11.

This document shows that Sri Lankan security forces were

warned about the threats.

Nothing is done to protect the churches.

These are the three cities where the attacks

take place on Easter Sunday.

In Negombo, around 8:45 a.m., security cameras

pick up this man walking into the St. Sebastian Church.

He's a suicide bomber.

This attack is the deadliest of the day.

Over 100 people are killed.

Around the same time, three separate other attacks

hit the capital nearly simultaneously.

One is here at a Catholic church

called St. Anthony's Shrine.

This dash cam footage gives a clue about the intensity

of the blast.

It blows off part of the church's roof.

At the Shangri-La Hotel's Table One Restaurant,

an Easter brunch is being served.

This photo is taken moments before two suicide bombers

strike that location.

The third target at this time is the Kingsbury Hotel.

Experts say the bombs reveal a high level of sophistication.

The amount of damage suggests the attackers

had expert bomb-making skills and access to military-grade

high explosives.

Each attack targeted confined spaces

maximizing the impact of the blasts.

Within a few minutes of the first waves of bomb blasts,

there are two more attacks —

one at another Colombo hotel, and another at a church

on the country's opposite coast.

As authorities respond, police encounter three more

explosives that detonate.

Three officers are killed in one of these instances.

So in the first 36 hours, six bomb attacks have occurred

and so have three detonations of bombs found by police.

[singing]

All of this proof that a very deadly day

could have been even deadlier.

[singing]