Detective Chief Inspector Phil Reade of Greater Manchester Police said: "This is a shocking case in which an innocent and defenceless little boy has suffered appalling injuries at the hands of someone who had been trusted to look after him.
"Rigby has today been put behind bars for a long time for his actions, but this will go little way to ease the suffering of Rio's family, who have lost their beloved little boy under such tragic circumstances."
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Donald Trump has branded those who take part in terrorist acts as "evil losers" in the wake of a suicide attack at Manchester Arena.
Live ITV News coverage after the explosion at Manchester Arena following a pop concert by US singer Ariana Grande.
What separates us from the terrorists is that we air our grievances with non-violent debate though our democratic structures and processes.