Prosecutors dropped the charges against the teen amid fears forcing his alleged victim, a 13-year-old girl, to give evidence about the incident at Perth Children's Hospital in January last year could worsen her mental health.
The boy was facing two counts of sexual penetration of a child and one charge of indecent dealing with a child before the discontinuance notice was accepted in September last year.
In detailing the case, prosecutor Brad Hollingsworth told the Children's Court the boy moved furniture and hid behind it in a bid to evade CCTV as he snuck into his alleged victim's room at 12.22am.
The teen allegedly raped the girl over several hours in the mental health ward where the pair were patients, as nurses shirked their duties.
They had gathered in an office out of fear of the boy, who had displayed concerning behaviour earlier in the day.
Mr Hollingworth said the girl known as Florence (not her real name) was admitted to the unit "because she had been sexually assaulted on two (previous) occasions and her mental health was unravelling".
He said that following the incident at the hospital she remained extremely vulnerable and at extreme risk of self-harm.
"The complainant's family is doing everything they can to keep her safe, but it is a day-to-day proposition at the moment, and someone must be with the complainant 24 hours a day," he said.
"Her parents cannot drive past this hospital without her being triggered and her becoming more emotionally unstable."
Mr Hollingworth said the trial would require Florence to give very detailed step-by-step evidence and could lead to dire consequences if she was forced to do so.
He also raised the prospect of Florence needing to be readmitted to the mental health ward in a bid to protect her if she gave evidence.
"Effectively, asking her to go back to the place at which this is alleged to have occurred," he said.
"That is not viable."
Mr Hollingworth said the prosecution could not ethically compel Florence to appear as a witness.
There was no prospect of a conviction and it was not in the public interest to pursue the case, he said.
WA Health Minister Amber-Jade Sanderson said on Tuesday the incident was devastating and preventable, and the health system had failed Florence and her family.
She also raised concerns over the staff members' failure to call hospital security for support.
The nurses and their supervisor faced disciplinary action over the incident.
The Child and Adolescent Health Service also conducted a review and the Office of the Chief Psychiatrist and the Mental Health Advocacy Service undertook two independent investigations.
Ms Sanderson committed to releasing the full recommendations from the Chief Psychiatrist's report.
WA Liberal leader Libby Mettam said on Wednesday the government should also release the other review findings and implement any recommendations.
"Previous reports had already highlighted serious concerns within this ward around staffing, sexual assault risks and the need for gendered wards," she said.
"The way this has been handled has decimated the trust and confidence of not only the family but the public and both have every right to know how this happened."
The Australian Nursing Federation called on the government to provide more information to Florence's family
"The victim and her family need these answers more than anyone," WA State Secretary Janet Reah said.
"Imagine this happening to your child and not knowing even the basics of what went on."
She also questioned the accuracy of reports nurses failed to perform their duties.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
Lifeline 13 11 14
Kids Helpline 1800 55 1800 (for people aged 5 to 25)
beyondblue 1300 22 4636
