Earlier the court was told that Rio's injuries were likely to have been caused by "heavy blows" from "punches, kicks, knees and stamping".
Simon Phillips QC, for the prosecution, accused Rigby of "striking Rio with such force as to split his liver in two" at around 4.30pm on April 22 this year.
He said the attack was part of "a sustained and violent attack".
He added: "A wicked attack on a defenceless two-year-old child."
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