Sentencing Rigby, Mr Justice David MacKay told him:
The jury has convicted you of the murder of this little boy. You don't need me to tell you what a terrible crime that was.
You abused that trust by punishing him physically in quite a revolting way.
It's a chilling, terrible picture. He suffered considerably before he died, I am satisfied. He was a vulnerable boy. You abused your trust.
The judge said he did not think Rigby intended to kill Rio but had a "sudden loss of temper" and "set about him, inflicting the fatal blow".