The suspect is a white convert to Islam who may have prior mental health issues. Not sure why the mainstream media has ignored this story, but here goes, from the Guardian:
A man suspected of attempting to carry out a terrorist suicide bombing at an Exeter restaurant received a text message of encouragement as he set out on his mission, counter-terrorism sources claimed today.
Armed police swooped on a second man in a cafe in Plymouth city centre today and arrested him in connection with the counter-terrorism inquiry.
The arrest came as further details emerged of the attack and the man believed to have carried it out. Nicky Reilly, 22, was injured when a nail bomb he is alleged to have been assembling partially detonated. He had gone into the toilets on Thursday lunchtime at the Giraffe restaurant in Exeter. Counter-terrorism officials believe the attack was intended to be a suicide bombing, two sources told the Guardian.
Reilly had a history of mental illness and police say he was preyed upon and radicalised. Detectives were looking for the person who sent the message of encouragement alleged to have been received by Reilly just before he left his Plymouth home and travelled by bus for more than an hour with the bombs.
More on Reilly's Islamist backers here.