The Manchester bomber employed a more “sophisticated” method of attack when he struck an arena packed with young fans of US singer Ariana Grande, experts have said.
The explosive device may have been packed with nuts and bolts, so-called “dockyard confetti”, to cause maximum damage, former police officer Chris Phillips said.
The counter-terrorism expert described the latest attack to hit the UK as “a step up”.
He told BBC Radio 4’s Today programme: “I think the point is that this was obviously a planned attack and that will involve people looking at the venue and seeing how the venue operates.
“And also the fact that it sounds like this was a strapped on suicide belt and also from what we just heard, perhaps, with what we call dockyard confetti which is the little bits of nuts and bolts that are attached to the vest.
“And those unfortunately are there deliberately to kill people and that’s the whole purpose of them.
“This does look like a step up and my worry, and I think the police’s worry now, is that this person probably wasn’t acting alone and there are other people that to be captured.”
Police have said they are investigating whether the suicide bomber acted by himself or was part of a network.
Former global terrorism operations director at MI6, Richard Barrett, said, while the attack was more sophisticated than recent ones, it does not automatically mean the person responsible was trained abroad to carry out the massacre.
He told Today: “I think people can build bombs, we have seen that in the past that it may be not that complicated to build a bomb which has an effect on the people immediately around you as this one certainly did.
“Yeah, sure that’s a bit more sophisticated clearly than driving a car into people or stabbing them with a knife but I’m not sure that it requires somebody to go to Syria for example, to have training there to get that sort of expertise so I’m sure the police will be very interested indeed to look at whoever is responsible, what he has been doing over the last months.”
He said the security services face a “real challenge” in monitoring potential threats and said investigations must involve “engagement” with communities.
He said: “I think in terms of additional security it’s much more on that intelligence side, on engagement with the community, on trying to understand better why people do this sort of thing than it is on putting up more bollards or, as you say, moving the choke point of security just a bit further away.”
He described the attack, targeted at concert-goers including children, as “very, very cynical”.
He added: “That is why it is so important to understand, I think, whether this person was connected with other people, whether it was in some way directed by an organised group.
“What was the intention behind it, in the broader strategic sense?”