"If any of it is true, he should be in jail" is why there is a trial. "He told me himself" is automatically accepted as a fact ? Any person with a grudge or a predisposition against the accused can simply say - yeah, he told me he actually did worse things and you would nod your head and say - yeah, proves my case - hang him ! Yes, if one of the girls came forward it would be helpful - if there are any actual girls to come forward. There is no proof with this statement.
I'm not questioning his guilt - I'm questioning the source of this evidence against him. Let's remove the disgusting nature of the crime and apply the same rules of evidence to any other court case. You are in court fighting a traffic violation - I come into court and tell the judge - She told me that she routinely speeds through school zones 100 kph over the limit and struck 4 kids while doing it. According to your theory, this deliberate fabrication should be considered when assessing your guilt.
I'm only in the peanut gallery but it does not seem like a valid source of evidence. You are accepting unproven facts as evidence.