The arrest of a Indigenous teenage girl in Western Australia was "unlawful, unreasonable, oppressive and unjust", the state's corruption watchdog says.
The Corruption and Crime Commission says it has concerns about the quality and outcomes of WA Police internal investigations into the arrest of the 14-year-old in 2022.
She was attempting to walk home late from a friend's house, pushing her electric scooter which had run out of power, when police in an unmarked vehicle stopped her.
In a complaint lodged by the girl's parents, it was alleged two officers pushed the teen to the ground, knelt on her back and handcuffed her before searching her bag.
They also demanded the girl provide a pin for a mobile phone to prove it was hers, which it was, said a commission report tabled in WA parliament on Friday.
She was allowed to leave the scene with her younger sister after one of the officers rode her scooter.
Body-worn camera footage showed the police involved - a male first class constable and a female probationary constable - were quick to escalate to the use of force, the commission said.
The girl's parents made a complaint to police alleging excessive force after she suffered a medical episode the following day and hospital staff identified swelling on her wrists, purportedly from the handcuffs.
WA Police initially found that the officers involved did not have sufficient grounds to request the girl's personal details.
But a second internal investigation reversed this, concluding that the officers had been entitled to reasonably suspect she may have been engaging in criminal activity, based on youth crime trends in the local areas.
The commission identified concerns with the second investigation, prompting police to conduct a third investigation.
This led to the officers being reprimanded for departing from various procedures, including handcuffing the girl for too long.
"The final investigation highlighted the interaction did not uphold the basic premise of policing, which should consider and maintain the rights and interests of the vulnerable, including juveniles," the commission said.
The investigation also concluded that the arrest had been lawful and the force used was reasonable.
The commission came to a different view.
"The arrest and subsequent force used were unlawful, unreasonable, oppressive and unjust," it said.
The commission also said the arrest "appeared hasty and the rationale was vague".
"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," it said.
The commission also said WA Police's management of the matter was inadequate.
"Its actions were incomplete, protracted and relied upon commission intervention to identify and address key issues, including not informing the girl's parent of the outcome of their complaint.
"The commission remains concerned with the conclusions reached by WA Police."
A WA Police response to a draft of the commission's report said managerial investigations have a centralised quality assurance process that includes an escalation mechanism to superintendent and then commander level.
"They agreed however, it was the commission's notice that led to a commander level review of this matter," the report said.
"In the commission's opinion, WA Police's quality assurance process failed to identify deficiencies in the investigation."
In a statement, WA Police said it had tens of thousands 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.
"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."
