Footage obtained by Sky News tracks the final hours of one of the Easter Sunday bombers as he prepares to commit mass murder.
It is the most detailed record yet to emerge of any of the attackers ahead of their coordinated strike against churches and hotels across Sri Lanka.
Islamic State has said it was behind the atrocity that killed more than 250 people.
Mohammed Nasar Mohammed Azar, 34, is pictured messaging and speaking on a mobile phone, praying at a mosque and scoping out his target.
The activity on his mobile phone offers evidence of a wider network possibly giving him instructions on when to mobilise.
He blew himself up at the Zion church in the east coast town of Batticaloa, a few miles from his hometown of Kattankudy.
The CCTV images capture Nasar Mohammed Azar arriving in the region on a bus just after 2am on Sunday morning.
He switches to a rickshaw, travelling for another hour until he pulls up outside the Jami Us-Salam mosque in Batticaloa.
The bomber leaves the vehicle and walks to the front gate of the mosque clutching two bags.
It is 3.13am. He can be seen waiting for the next two and a half hours, at times pacing up and down and checking his phone.
At one point a police car drives up, but the officers inside either do not see Mohammed Azar or he does not arouse their suspicions, and it pulls away.
At 5.42am the gate of the Jami Us-Salam mosque is opened, allowing the attacker to enter.
He can be seen walking inside the compound with his bags, presumably containing a suicide bomb, before finding a place to leave them, re-emerging with what looks like a washbag.
He enters a bathroom area to have a wash before striking up a conversation with someone else in the mosque.
Just after 6am he joins fellow worshippers to pray, before slipping away early, one hand in his pocket again.
Next, he is shown in colour pictures, in a bright blue T-shirt and black tracksuit bottoms, praying alone between two plastic chairs.
Then he changes into the outfit he will wear for the suicide mission - an orange top, a beige cap with an energy drink logo on it and a rucksack.
It is the same style of rucksack used by the other bombers.
He appears to be staking out his target, speaking on the phone and walking slowing.
It is only minutes until the first suicide bomb goes off in Colombo.
At around that time, Nasar Mohammed Azar is pictured back at the mosque, having switched back into his blue shirt.
He fetches what look to be a pair of laced shoes and socks, before going to the bathroom one last time.
Just after 9.30am he emerges again with the orange shirt, baseball cap and backpack.
As he exits the mosque, he digs a mobile phone out of his pocket, looking at the screen and seemingly writing a message.
He strides casually along the street, steps over a cordon, and disappears out of shot.
The moment of the attack is not shown in these images.
A week on, the faces of Nasar Mohammed Azar’s victims - including 13 children - stare out from banners pinned up in mourning outside the Zion church.
Nasar Mohammed Azar’s home town of Kattankudy is the birthplace of Mohammed Hashim Mohammed Zaharan, the suspected ringleader of the suicide bombers.
A security source said the two men were friends.
They had both been living away, but Nasar Mohammed Azar reappeared three days before Easter.
He travelled in and out of the area in the final stages of his assault.
His mother has since been arrested after she allegedly burnt documents, including photographs of her son, according to a source.
Source: Sky News
-Agencies
