The most chilling footage to emerge from Sri Lanka's Isis-linked terror attacks came from CCTV and church cameras.
A man with a large backpack walks towards and then alongside St Sebastian's Church in Negombo. He pats a young girl on the head. He passes pews of worshippers. He finally walks inside.
The video cuts out and the man detonates the nail-studded bomb in his pack, killing more than 100 people. Other churches and hotels were targeted by bombers with backpacks too.
What jumps out from the footage is the bag, which should never have got near a congregation at Easter. Surely someone should have noticed. Surely he should have been intercepted.
Since 9/11 the world has become used to increased security. Subsequent attacks in Madrid and London involving bombs in backpacks drove lessons home. We've all become used to bag searches at any public event and multiple suitcase checks at airports. We've become wary — mainly as tourists in unfamiliar surroundings — of the sight of large bags in crowded areas.
Other weapons have been used in terror attacks — trucks, cars, semi-automatic rifles — but the threat of bombs in bags has remained, as the 2017 Manchester blast showed.
Places of worship by their nature are instinctively embracing. The Christchurch mosque suspect was greeted with "hello, brother". Shooter Dylann Roof was welcomed into a black Charleston church's Bible study group. But the Sri Lankan Government says intelligence warnings of an attack on churches, received days before Easter, weren't passed on to senior levels.
Negombo was a potential target for anyone wishing ill against Christians in Sri Lanka. Of its 140,000 residents, 65 per cent are Catholic. A "beef-up security" alert for Easter could have made a major difference.
The general impression is of complacency, especially since the Christchurch attack was just weeks ago. The complexity of the co-ordinated Sri Lankan attacks suggests that planning for them was under way before March 15. But in the aftermath of Christchurch, experts who study terrorism warned that both white supremacists and jihadists would use it as a recruiting tool. And the idea that Isis would bring a bombing campaign to the rest of the world after its caliphate ended has long been discussed.
All governments and their security services should have been awake to threats.
Prime Minister Ranil Wickremesinghe said the Government knew Sri Lankans who had joined Isis had returned but they could not be arrested because joining a foreign terrorist group was not illegal. But they could have been put under surveillance or questioned or held for other crimes.
Researcher Charlie Winter, who studies radicalisation, tweeted: "We are likely to see more attempts at attacks more regularly for the foreseeable future. Sri Lanka was not a one-off. If anything, it was a test-run."