A man who was convicted of forcing his six-year-old brother to have sex with him when he was a child has been acquitted by the nation's highest court.
The man, known only as RP, was 11 when the offences took place in two separate incidents in 2005.
When no adults were home, he grabbed his half-brother, held him down, covered his mouth and had intercourse with him, stopping when he heard an adult return and telling the younger boy not to say anything.
He did it again a few weeks later.
Children under 14 are presumed to lack the capacity to be criminally responsible for their actions.
But RP was convicted of two counts of sexual intercourse with a child after the judge found it had been proved he knew his actions were seriously wrong in a moral sense.
RP later appealed but it was dismissed by the NSW Court of Criminal Appeal.
The High Court on Wednesday ordered his convictions be quashed.
It referred to evidence heard in RP's trial that, as a teenager, he was twice assessed as being borderline disabled when it came to his intellectual functioning, with the original judge finding him of "very low intelligence".
The High Court found that in the absence of evidence about the environment in which RP was raised or his moral development at the time, and given his intellectual limitations, it was not open to conclude beyond reasonable doubt he knew his conduct was seriously wrong in a moral sense.