Cassidy Trevan suicide
Cassidy Trevan, 13, committed suicide after being subjected to years of abuse by bullies who lured her to a house where she was gang-raped Cassidy Trevan/Facebook

A heartbroken mother has shared the tragic story of her teenage daughter, who committed suicide after being bullied by a group of girls, who lured her to a house where she was gang raped.

Linda Trevan described how her 13-year-old daughter Cassidy was subjected to a relentless campaign of emotional and physical abuse by a group of bullying girls at the Melbourne high school she attended.

Her mother told 9 News that the girls would slap her on the face, leave banana peels at the door of their family home and regularly subject her to abuse on social media.

The ongoing attacks resulted in her missing her fourth term of Year 7 at a Melbourne high school. When she returned to school, attending for just two days a week, the bullies appeared to be remorseful and apologised for their behaviour.

Feigning friendship, they then invited her to a festival, but instead of going to the festival, they led her to a nearby house where two older boys lay in wait.

"They were older boys that Cass didn't know. Two girls who sat and waited. Two boys who shared her and timed each other. One boy stood guarding the front door," Linda told 9 News.

While Cassidy and her mother met with Detectives from Victoria Police's Sexual Offence and Child Abuse Investigation Team (SOCIT) over 20 times during a two-year period, Cassidy never made a formal statement to Dandenong police .

The devastated mother said fearing reprisals, Cassidy refused to report the attack amid concerns that recounting her ordeal would 'push her over the edge.'

While Cassidy moved school, even after the attack the key bully continued to subject her to verbal abuse online. "I had to get an intervention order on the main bully girl when she physically assaulted Cass at the shops, after the rape, and she was even calling my mobile demanding to talk to Cass," Linda told 9 News.

Cassidy Trevan suicide
Cassidy's mother Linda said the bullies have their daughter's blood on their hands Linda Trevan/Facebook

In a heartbreaking open letter to the bullies on Facebook, Linda described her daughter's torment as she spent the next two years 'desperately doing everything' she could to keep Cassidy alive.

"I had to watch my baby suffer for the next 22 months from these demons," she wrote online. "She worried you would find her and get her again, she went through continued bullying from some of you who managed to get to her by phone or social media, via others, even after what you'd done to her.

"She suffered flash backs of the crime, nightmares, insomnia, separation anxiety, panic attacks, PTSD and subsequent worsening mental illness.

"I helplessly watched my precious child wither away before my eyes, mentally & physically, until she rarely got out of bed, until she could no longer take the pain and torment you caused her," she wrote.

Cassidy committed suicide on December 12, 2015. Addressing her abusers Linda told them they had "blood on their hands."

"What you did to her was a direct cause of her suicide on 12th December 2015," she said.

"I know who you are, you know who you are, and the police know who you are. I hope the knowledge of what you did haunts you for the rest of your lives, and one day, if you are lucky enough to have children of your own ... remember what you did to my precious only baby, and imagine how you'd feel if someone did that to your baby.

"I'm not a mean, angry, or vindictive person ... but what you kids did ... I hope you never forgive yourselves and never forget the name Cassidy Trevan. You all have blood on your hands for as long as you live.

"Bullying killed my child, bullying must be taken seriously."

According to Mail Online, a spokesman for the Victorian Department of Education told Daily Mail Australia: "The death of any young person is an absolute tragedy and our sympathies are with Cassidy's family.

"Schools have a range of ways to help students who may be experiencing bullying or mental health issues, including by providing qualified counsellors. School staff work hard to identify and support students who need support and we would encourage any students who need help to talk to staff at their school."