A 15-year-old boy has admitted to raping an 84-year-old grandmother before forcing her to shower in front of him to wash the evidence away.

The Perth boy, who cannot be named, pleaded guilty to the horrific sex attack in court on Tuesday after breaking into the woman's home on October 13.

Police said the teenager broke into her home at Waikiki, an outer suburb of Perth, at about 5am while she was asleep and raped her three times, 9 News reported.

He then stole property and fled the scene, but was arrested by police two days later.

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A 15-year-old boy (pictured) has admitted to raping an 84-year-old woman in Perth

West Australian forensic police are pictured at the scene of the violent sex attack

A law enforcement source told Daily Mail Australia the boy was on parole at the time of the sickening attack.

The repeat offender was arrested numerous times last year for stealing and once for robbery before being jailed in late 2016.

After release he committed other offences while on parole and was jailed again.

The boy's older cousin told Daily Mail Australia the rapist was recently released from Banksia Hill Detention Centre after serving time for stealing a car.

Banksia Hill, about 20km south of Perth's CBD, is Western Australia's only detention centre for offenders aged 10 to 17.

The pair met about 10am on October 13, just hours after the alleged crime, after the boy returned to Perth from staying with his uncle in south-west Western Australia.

'I picked him up and later on we went to a party and then went home, but I took off in the morning,' the cousin said.

The cousin said the boy was not acting out of the ordinary and was just happy to be home after serving his time.

Police were called to the scene of the rape of the elderly Perth woman on October 13

The rapist was recently released from Banksia Hill Detention Centre (pictured) after serving time for stealing a car

'He was just normal, quite like how he his all the time,' he said.

The young man who spoke to Daily Mail Australia admitted his cousin had a history of burglaries, stealing from cars and other petty crime.

'He only does it with other people though, never by himself,' he said.

'He's just in with the wrong crowd.'

The cousin said the boy didn't go to school and was on welfare, and bounced around the houses of family and friends.

The elderly woman was badly injured and severely traumatised after the attacker broke in while she was sleeping.

She was home alone when the teenager smashed his way into the house and pinned her to the ground.

Forensic police searched the woman's home for evidence including her attacker's DNA.

The woman was taken to Perth's Fiona Stanley Hospital and later released.