A few years ago, Reilly converted to Islam and adopted the name Mohamed Rasheed. He attended several mosques around his home in Plymouth, about 50 miles from Exeter, and hung out with a predominantly Kurdish and Turkish group of men at a fish-and-chips shop near the apartment where he lived with his mother.

Police have not revealed details about the process by which he was allegedly recruited and radicalised. But May 22, he rode a bus to Exeter carrying three crude explosive devices described as nail bombs capable of causing a fireball-type explosion. He entered the Giraffe restaurant, which is popular with families, around lunchtime and went into a bathroom in back.

One of the bombs went off prematurely as Reilly was allegedly handling it, inflicting severe burns and cuts on him, authorities said. Footage from security cameras showed him staggering out of the restaurant, his face and shirt bloody, as patrons fled in panic. Investigators say the bombs could have caused casualties if they had been set off properly.

Anti-terror officials say it is another sign that extremism in Britain has spread among an increasingly young and diverse population.