Nathaniel Okusanya, received a life sentence with a minimum term of 20 years.
Nelson Idiabeta, detained at her majesty's pleasure, received a minimum term 19 years
Passing sentence his honour Judge Marks QC told the two teenagers:
"You have shown not one iota of remorse, both of you seeking to brazen it out in front of a jury."
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The 47-year-old man died shortly after 3pm on Tuesday.
Specialist explosive detection dogs searched through the town examining letter boxes and phone booths for signs of potential devices.
Temperatures reached 29.1C in St James's Park, central London.