There was an old chicken shed at the Quamby youth detention centre. Out past the classrooms and out of sight of the facility's many security cameras, it was a place most detainees avoided. But they knew what sometimes happened down there.

"He'd only take one at a time down to the chicken shed," says James*, a young Indigenous man who spent 22 months locked up in Quamby before the facility was shut down by the Australian Capital Territory due to human rights concerns. "That's where he'd sexually assault me, and I'm pretty sure he'd been doing it to other boys but it went on for ages." The man who James alleges took him to the chicken shed was a detention centre guard named Brett Dennis. Everyone knew him as Chicken.

At least 12 other former detainees of the ACT's youth justice system between 2003 and 2013 allege that Dennis sexually abused them.

"He would always take the boys down to the chicken shed on weekends and do shit down there," James says. "There were other times where I'd be strip-searched and be assaulted there as well." James was 14 when he was first incarcerated in Quamby in the early 2000s. His upbringing was marred by domestic violence and he was in and out of foster care, before he began dabbling in drugs and alcohol, and stealing cars.

He is speaking to Guardian Australia via a video link from a drug and alcohol rehabilitation centre – his attempts to blunt the trauma have billowed into a lifelong struggle with addiction, substance abuse and suicide attempts. He still has nightmares, 20 years later. "Everyone knew something was wrong," he says.

"I kept on trying to knock myself, hang myself, because of what happened. "I was quiet at the time.

I should have spoke up back then but I was living in fear. [But] if I had said something, then they wouldn't have believed me." 'He gave me my first hit' Dennis worked at Quamby, and later its successor, the Bimberi youth justice centre, until a few years before his death from suicide in 2017. The ACT government, in a statement to Guardian Australia, said it was not aware of any allegations of child abuse made against Dennis before his death.

Quamby was built in 1962 and incarcerated children as young as 10. It closed in 2008.

James is one of 22 plaintiffs to have lodged civil proceedings alleging historical sexual abuse by staff and by fellow detainees at the Quamby or Bimberi youth detention centres, now before the courts, with the ACT government named as a defendant. The territory's government is also responding to 31 personal injury claims related to historical child sexual abuse allegations, which are at the pre-court stage.

Four of those young men have spoken to Guardian Australia. They give eerily similar accounts, despite their experiences being separated by years and occurring at different centres. They allege they were not believed, were dismissed or had no way of disclosing their abuse at the time.

Court documents reveal that Dennis held a series of short-term rolling contracts with the ACT government as a youth justice officer before he was made a permanent employee in August 2006, and continued working in the system until about 2015. Former detainees at Quamby and Bimberi describe a man with a peculiar mix of warmth and unyielding power. Kind words and a friendly ear in a quiet corner are talked about in the same breath as allegations of choking, forcible strip-searches and physical assaults, as well as claims he supplied detainees with drugs, confectionery and cigarettes.

David* met Dennis on one of his first nights incarcerated as a teen in the Quamby centre.

"He gave me my first hit [of ice]," he says, recalling the night for Guardian Australia. The darkness of his cell was broken by torchlight beaming into his eyes, then pointing toward the ground in front of the slot on the door, where something had been dropped. "He didn't say anything to me … There was a little bag.

I didn't even know what it was." David tried the drug. "That was the end. I was fucked." In documents filed in 2025 with the ACT supreme court, David alleges he was sexually abused by Dennis on several occasions, supplied with and encouraged to use methamphetamines, and raped five times. He alleges that the ACT government breached its duty of care to protect him from abuse, failed to implement a "safe system of care" for a vulnerable child, knew or ought to have known about the general risk of abuse of detainees within its institutions, and should have taken precautions to avoid the risk of harm.

Those precautions, the statement of claim says, should have included maintaining a system in which children were encouraged to report misconduct to those in authority, the removal of abusive staff and implementing mandatory reporting of child abuse or suspected child abuse, and appointing a representative to safeguard children.

In response, the ACT government admitted that it had a duty of care but denied it had failed to take reasonable precautions to protect children, saying mandatory reporting obligations and an official visitors program were in place at the time of the alleged offending.

It admitted that there was a risk of physical or psychological harm if the complainant was assaulted by a Quamby employee but "denies it knew or ought to have known of a risk posed by Brett Dennis to the plaintiff".

It's the same wording used in response to other claims submitted by people who have spoken to Guardian Australia, who allege Dennis assaulted them.

Sexual abuse cases naming workers at the Quamby and Bimberi youth detention centres began to trickle in several years ago, with dozens of victims alleging sexual abuse, rape and assaults. The allegations span 40 years.

Kirsten Nasser, from the legal firm Maliganis Edwards Johnson, is a solicitor and personal injury lawyer who has handled hundreds of civil compensation claims over more than a decade, specialising in cases alleging institutional abuse. The allegations concerning Canberra's youth justice system show a familiar pattern, she says.

Staff members knew children were suffering and some who spoke up were ridiculed, she alleges. "It seemed to be a bit of a protect-the-perpetrators club there … The few that did [speak up] were shunned out." Michael* met Chicken when he was locked up for one night at the age of 16. Over the course of that night he alleges he was sexually abused and raped.

"He took me down to the chicken shed," Michael says, shifting in his seat, his eyes fixed on the wall behind us. "I thought it was normal. I really was only a kid. It fucked everything. It changed my whole life. I don't trust anyone." He says he still lives with the trauma of what happened that night in Quamby, spending the next few years in and out of jail for drug offences. The jangle of keys or seeing the word chicken can trigger a flood of memories of the alleged abuse.

He ruefully acknowledges he entered the youth justice system as a "little shit who didn't know anything" but says that when he tried to tell adults what had happened his allegations were dismissed. "I tried to tell the courts with my next appearance," he says. "No one believed me. Who's gonna believe a little shit kid?" Michael has filed a claim against the ACT government. In its response, it confirmed that Michael had been held for approximately 14 hours on the day of the alleged rape but denied any knowledge or admittance of the allegations of abuse.

In response to detailed questions from Guardian Australia, an ACT government spokesperson said it "recognises that historical allegations can involve complex trauma and acknowledges the significant impact that revisiting past experiences may have on individuals".

"Where matters are before the courts, support arrangements will depend on the circumstances of each case and the services with which an individual is engaged," the statement said.

It added that the ACT funded a range of "trauma-informed counselling, mental health and victim support services that may be available to eligible individuals" and that as the defendant to these claims, it was "also responsive to requests from claimants or plaintiffs for counselling or psychological sessions to be funded at the outset of such processes in recognition of the benefit such services can provide, and the complex trauma involved".

Accusations of stonewalling Nasser's firm represents 30 clients who allege they were mistreated or abused while in ACT youth detention. Its lawyers claim that the territory government has been withholding critical personal records and stonewalling their clients' civil cases.

"That's why there's been such a delay in the proceedings that we have on foot at the moment," Nasser says. "They're taking 12 to 18 months or two years to get us records that relate to our clients. "I've worked for clients who've experienced institutional sexual abuse from religious organisations such as the Catholic church and the ACT government's response is worse." The years-long legal process and frustration when seeking access to basic records has been traumatic for clients, Nasser says. She claims it runs contrary to the ACT's commitment to being a model litigant adopted after the national royal commission into institutional responses to child sexual abuse.

The royal commission heard from more than 6,500 survivors, 8% of whom were abused in youth detention. The numbers were greater for First Nations survivors, more than 15% of whom said they were abused in youth detention.

For many clients, Nasser says, the alleged sexual abuse was "the nail in the coffin for their trajectories in life". "They then use drugs and alcohol or substances as a way to cope with that trauma, that violation to their bodies, and it ends up affecting them for the rest of their life." The ACT government said it was "conscious of its obligations as a model litigant to act honestly and fairly" in responding to claims, "in particular the sensitivities of claims of this nature". It added: "The traumatic and sensitive nature of claims arising from allegations of historical child abuse notwithstanding, the ACT Government must undertake investigations into all allegations made and respond in accordance with legal principles."

The spokesperson said: "Questions of liability in such matters are often complex and are considered on a case-by-case basis." Assessing historical records took time and the government was "working to provide relevant records as quickly as possible while meeting our legal and privacy obligations".

Guardian Australia has spoken to a number of people who worked at Quamby and Bimberi in the same years as Dennis. They declined to speak on the record. One former employee claimed that they knew of several people who were abused by former staff or detainees. Another told the Guardian they had not seen any concerning behaviour by staff toward detainees.

Some former guards have come forward to Nasser with statements that corroborate survivors' stories of physical and sexual abuse, she says, including alleging that incident reports or internal memos were suppressed or altered when concerns were raised internally.

A 2011 inquiry into the Bimberi facility – established in 2008 after an audit found widespread human rights concerns including the use of inappropriate force and excessive strip-searches at Quamby – found that there had been flawed record-keeping and there was evidence of records being altered, including the deletion of records of "significant disturbances". It also raised serious concerns that there was no record of verbal or written complaints in a or central database.

"It is most concerning that several people claimed that some records of complaints 'were destroyed', 'were not investigated' or 'went missing'," the inquiry found. "While these allegations are not corroborated by independent information, we note that a strong record keeping system for complaints at Bimberi would enable [the ACT's Community Services Directorate] to dispute any accusations of complaints going missing."

'I can't escape it' Brian* was 12 when he was first locked up at Bimberi in 2008. He was jailed again in 2013. In documents filed with the ACT supreme court, he alleges that Dennis sexually abused him on multiple occasions. The assaults happened at night in his cell, he alleges. On several occasions, he says, Dennis allegedly rubbed his genitals over his clothing. He also alleges he was digitally penetrated by Dennis, and in the final incident he alleges he was raped in his cell.

Now 30, Brian says the abuse destroyed his life and he turned to drugs and alcohol. "Drugs took over my life," he says. He's speaking to Guardian Australia from his lawyer's office. His breaths are shuddering gasps as he clutches soggy tissues and chews Red Ripperz lollies.

"I see his name everywhere," he says. "He's got the name Chicken, I'll see KFC and it's chicken.

I can't escape it. "They're supposed to be looking after you, and they do that fucking shit to you. You got no one to call out to for help. It's pretty fucking bad.

"Some of the workers were good, I got along with them, but then you didn't know who was in with who."

Nasser says her clients just want recognition. "They just want their moment of someone coming along and saying: 'I'm sorry, we're taking this seriously. We acknowledge that wrongs were done to you, and this is how we're moving forward.'" *Names have been changed Indigenous Australians can call 13YARN on 13 92 76 for information and crisis support; or Lifeline on 13 11 14, Mensline on 1300 789 978 or Beyond Blue on 1300 22 4636. Support for anyone affected by rape or sexual abuse is available at Full Stop Australia on 1800 385 578. Children, young adults, parents and teachers can contact the Kids Helpline on 1800 55 1800. Adult survivors can contact the Blue Knot Foundation on 1300 657 380. Other international helplines can be found at befrienders.org Do you know more? Contact australia.indigenous@theguardian.com