Two boys aged 11 and 13 have been released on bail following their arrest on suspicion of having unlawful sex with an 11-year-old girl in a case set to test the way Hong Kong deals with sex crimes involving children. The boys - who could face life in prison as a result of a change to the law in 2012 that abolished the presumption that males under the age of 14 were incapable of sexual intercourse - were detained on Thursday night after the 13-year-old was found having sex with the girl as the younger boy filmed them with his mobile phone in the stairwell of a Tuen Mun public housing estate. The younger boy allegedly had sex with the same girl earlier. They were discovered in Hing Yiu House, Tai Hing Estate, by a security guard who called police. The maximum penalty for sex with a girl under 13 is life in prison - the same as rape - while the maximum sentence for sex with a girl under 16 is five years. It is understood defendants cannot argue that consent was given in their defence because the laws are set out to protect extremely young girls. This landmark change was made after a legal and public outcry five years ago over a case in which a magistrate described laws for juveniles and serious sex offences as "wholly and manifestly inadequate". She convicted a 13-year-old boy on the lesser charge of indecent assault and sentenced him in 2011 to a reformatory for a "disgusting" sex attack on a five-year-old girl in a hospital ward in Chai Wan. That case prompted the Law Reform Commission to recommend that the age threshold of 14 for unlawful sexual intercourse be lifted. However, under a legal principle called doli incapax , prosecutors must prove boys aged between 10 and 14 know what they are accused of is "seriously wrong", not just "naughty or mischievous". Senior government counsel Thomas Leung, secretary of the commission's subcommittee reviewing sexual offences, said it was a rare case and young offenders were seldom jailed. The Department of Justice was unable to provide figures on how many sexual assaults involving boys under 14 it had prosecuted since the amendment. The guard stopped the boys at the scene, but the girl had left. She was found by police and examined in hospital. Officers seized the phone the boys used. It is understood the younger boy and the girl are Primary Six pupils at the same school while the older boy is a Form One pupil, and that the 11-year-old introduced the girl to his older friend. "So far there is no evidence to suggest the girl was forced to have sex with the two boys," a police source said. The boys have been released on bail and will report back to police next month. In 2009, two 13-year-old boys were convicted of indecently assaulting a 12-year-old girl despite evidence of intercourse between one boy and the girl.