Footage provided to CNN shows a man identified as a suspect by Sri Lanka state TV SLRC walking around St. Sebastian's church on Easter Sunday morning, shortly before it was rocked by an explosion.
The blast at the crowded service in Negombo was one in a series of coordinated attacks -- which targeted churches and luxury hotels within minutes of each other -- across the country.
What you can see: The suspect can be seen carrying a large backpack as he makes his way across the courtyard towards where the busy service is already underway.
At one point, the alleged bomber can be seen briefly stopping to pat a child on the head before continuing on his way.
Making his way through the throngs of people perched outside the service, he enters a side door of St. Sebastian's, close to the altar.
The next frame, according to police but not provided publicly, shows the suspect detonating his bomb.
Sri Lanka police said they would not comment on the video until the conclusion of the investigation.