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."
More top news
A shot of a chameleon using its tongue to grab dinner has snatched a top photography award.
One story dominates Thursday's front pages with some newspapers printing emotive pleas to voters to keep the United Kingdom as one.
After a mild start temperatures should pick up, with the south of England seeing highs of 26C.