A man who raped his six-year-old brother when was 11 has had his conviction quashed, after the Australian High Court found he could not have understood that his actions were "seriously wrong".

The man, who is only known as RP and from the state of New South Wales, was convicted after raping his younger brother twice in 2005.

But, now aged 22, he has been acquitted by the High Court, according to The Australian. In its judgement, the court noted the perpetrator had a lower IQ than 96% of his peers when tested at the age of 18.

According to the High Court report, when RP was left to babysit his younger siblings a decade ago, he locked the six-year-old in a room and said: "If you wanna come out, you gotta let me do this to ya."

He then smothered the child's mouth and raped him, as the boy cried out "no, no". When the father returned and found them, he warned the six-year-old: "Don't say nothing."

The father left the children alone again just a few weeks later, at which time the older boy exposed his penis to his brother before raping him again on a pile of clothing.

In Australia, children aged from 10 to 14 are presumed to be doli incapax, or incapable of legal wrong. The same defence used to be in force in Britain, but was struck out in 1998.

This right can be over-ruled if a child is believed to understand their conduct is seriously wrong. RP was therefore found guilty a decade ago

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But subsequent intelligence tests, and the assessment of a clinical psychologist that the child's upbringing was "fairly unsatisfactory", led the High Court to reverse the earlier judgement.

The judgement read: "I am left... with a reasonable doubt about whether RP understood that the sexual intercourse which he had with his brother was seriously wrong by normal adult standards."

The Independent has contacted the Australian High Court to establish whether the man was still serving a custodial sentence, and if so, whether he has now been released.