The bomb which exploded outside Liverpool Women’s Hospital contained ball bearings and could have caused “significant injury or death”, counter-terror police have said.
It has also emerged that the bomber, Emad al Swealmeen, spent many months buying ingredients for the device and used a series of aliases.
His brother has been interviewed to gain an “insight” into his state of mind.
Police have spoken to bomber Emad al Swealmeen’s brother
In an update, officers from Counter Terrorism Police North West said the bomb was made using “homemade explosive” and the ball bearings “attached to it would have acted as shrapnel”.
“Had it detonated in different circumstances we believe it would have caused significant injury or death,” said Assistant Chief Constable Russ Jackson.
How or why the device exploded when it did are still being determined, and officers are “not discounting it being completely unintentional”.
Mr Jackson added: “It is a possibility that the movement of the vehicle or its stopping caused the ignition.”
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Detectives are spending “considerable time” trying to understand the approach bomber Emad al Swealmeen used as he purchased the ingredients for his device.
“This is complicated because purchases have spanned many months and al Swealmeen has used many aliases,” Mr Jackson said.
“We are confident, however, that in time we will get a full picture of what purchases were made and how, and if anyone else was involved or knew what al Swealmeen was up to.”