Residents said a suspicious character had first gone to the St Mary's Catholic Cathedral on the same road opposite St. Michael's Boys' School half hour earlier and a Catholic priest said he saw the suspect lurking around the complex the previous day as well.
The priest in charge had called the Easter Service at St Mary's early and it began at 7am, instead of the normal 7.30am. So, by 8.30am when the suicide bomber arrived, most of some 1,000 who had congregated had left.
When the bomber learnt that the mass had ended, he made his way to the smaller Zion Church, raising speculation that his initial target had been the St Mary's Cathedral, residents were quoted as saying.
Relating his encounter with the suspect, Pastor Ganeshamoorthy Thirukumaran or Pastor Kumaran of Zion Church said: "I noticed a person standing near the pastor's office, with a bag on his shoulder and clutching another bag to his chest.
"I asked him who he was, and why he was standing there. He replied that he had just come to observe what was happening at the church and asked me details about the church."
Upon further questioning, the man, who looked in his 30s and was of medium height, identified himself as 'Umar' from the nearby Oddamaavadi Town, Pastor Kumaran said, the Mirror reported.
"I then invited him into the church as I thought he was like the many new people who come to our church. I didn't have any doubts or suspicions about him."
Pastor Kumaran told a senior worshipper, Brother Stanley, to speak to the visitor. The suspect's questioning and demeanour resulted in Brother Stanley trying to lead him out of the church premises.
The man then tried to force his way into the church. When his path was blocked, he reportedly detonated the bomb just outside the church and close to a group of children.
Pastor Kumaran's son was among the children who died in the explosion.
Residents said that if the man had entered the church building which had two floors and then had about 500 worshipers inside, the death toll would have been higher.
According to Batticaloa Division Police Superintendent Nuwan Mendis, the head of the suspected bomber was found on the roof of a house near the church.
The Mirror quoted him as saying that investigators were trying to identify the killer through CCTV footage "and other methods".
The Zion Church was one of three churches and three luxury hotels which were targeted near simultaneously by suicide bombers on Easter Sunday, killing 359 people and wounding hundreds.