Western Australia's Crime and Corruption Commission has slammed the arrest of a 14-year-old Aboriginal girl by WA Police, labelling the actions of officers as "unlawful, unreasonable, oppressive, and unjust".

The CCC described internal investigations by WA Police as "inadequate," noting without the CCC's intervention, "[they] would have failed to adequately address the allegations of serious misconduct".

The girl was arrested in March 2022 while walking home from a friend's house late at night and pushing her electric scooter, which had run out of battery.

Police in an unmarked vehicle saw her when she was close to home, pushed her to the ground, knelt on her back, and handcuffed her.

In a highly critical statement, the CCC said: "The mere fact of a juvenile walking late at night with a backpack does not objectively provide a reasonable basis for suspecting that they had committed, or would commit, an offence".

The two arresting officers - a male first-class constable, and a female probationary constable - found a mobile phone in the girl's bag and asked for the PIN so she could prove it was hers.

She did this and was allowed to leave with her sister - also a juvenile.

One officer rode the scooter before returning it.

Whilst the officer said he checked that the handcuffs weren't too tight, body worn camera (BWC) footage revealed the girl complaining of pain as she was asked for her name.

Both officers turned off their BWC with the girl still in handcuffs and seated on the kerb.

Whilst it didn't show everything, the CCC said the BWC "does illustrate a quietly spoken Aboriginal girl, who asks what she has done wrong and the reason why she is being arrested".

"During the incident the girl says very little, but when she does speak, she appears calm and quietly spoken," the CCC said.

The next day, the girl suffered a medical episode and when staff at the hospital found swelling on her wrists, she revealed she'd been arrested and her parent - who was unaware of the arrest - made a complaint to the police.

The location of the arrest has not been revealed.

The CCC noted whilst an initial investigation by WA Police found the officers did not have sufficient grounds to request the girl's personal details, a second investigation reversed this, concluding the officers had been entitled to "reasonably suspect" that the innocent 14-year-old walking home may have been engaging in criminal activity, "based on youth crime trends in the local areas".

"Irrespective of the lawfulness of the arrest, the male officer's actions were noted [in the second police investigation] to be concerning," the CCC said.

"It appeared he was swift to react by using force, particularly as the BWC vision was inconclusive as to whether the girl attempted to walk away."

After being notified of the outcome of the investigation, the Commission said they identified "concerns over the officers' arrest powers," which prompted a third internal investigation by the police.

This culminated in the officers being reprimanded for their departure from several procedures - including handcuffing the girl for too long, the officers not providing the girl with her rights, and failing to correctly record a smoking implement.

However, this investigation also concluded the arrest lawful, and the force used reasonable.

The female officer was given a reprimand, and the male officer given a warning notice, with the CCC highly critical of the entire process, which took 18 months.

The girl's parent was not notified of the outcome.

The Commission said they were prompted to conduct a "comprehensive review" of the incident and internal police investigations.

"WA Police's actions were incomplete, protracted and relied upon Commission intervention to identify and address key issues," the CCC said, "including not informing the girl's parent of the outcome of their complaint".

"The Commission remains concerned with the conclusions reached by WA Police.

"However, the Commission does not have the power to substitute its own view for that of WA Police, which is ultimately responsible for preventing, identifying and responding to misconduct risks within its ranks."

They took a different view to the legality of the arrest than that of WA Police - who argued the force was reasonable, other than the handcuffs being applied for too long.

"If the arrest is unlawful, then any force used during it is therefore also unlawful," the CCC said.

The CCC said the officers exhibited "limited verbal de-escalation, and a rapid and unnecessary escalation to use force".

This was, the CCC argued, backed up by the junior female officer, who said she would have used verbal skills instead of the same use of force as her colleague.

"Both officers failed to comply with the required procedures when dealing with a juvenile. Furthermore, the officers did not demonstrate a genuine concern for the girl's welfare," the CCC said.

"The girl's welfare was not seen as a priority, which would have been a reasonable basis for stopping, enquiring, and assisting her to get home safely."

In a statement, WA Police said it had a large amount of positive interactions with young people every year.

"We don't always get our interactions with young people right, but we must and will always strive to do so," a spokesman said, via AAP.

"Our professional standards unit and oversight functions such as the CCC are there to ensure we are transparent and to continually improve the way we police here in WA."