For Jerry Cooper and the friends he knows as the White House boys, the memories never fade. The brutal beatings, rapes and other physical and psychological abuse they endured at a notorious Florida reform school were more than half a century ago, but there is always something to trigger the flashbacks.

This time, it was the discovery of 27 “possible” graves at the site of the Arthur G Dozier School for Boys in Marianna, Florida, where Cooper and others saw classmates, some no older than 12, simply disappear in the middle of the night.

It is no surprise that more victims of systemic, decades-long sexual abuse and violence could still be in the ground. A study that ended in 2016 saw University of South Florida (USF) anthropologists uncover human remains in 55 graves, several with gunshot wounds or blunt force trauma.

I told them for years there’s a lot more boys dead than the 55 they located. We’ve always known this Jerry Cooper

Yet to the White House survivors, named for a whitewashed cottage in the grounds of the state-run school where the worst of the abuse took place, it was confirmation that the final chapters of a dark episode have yet to be written.

“I got the worst beating I ever got at that school, over a hundred lashes at two o’clock in the morning, searing the cloth of my nightgown and my underwear into my skin. I was sure I wasn’t going to survive,” said Cooper, 74, who spent two years at Dozier as a teenager in the early 1960s.

“But there were those of us who didn’t. I told them for years there’s a lot more boys dead than the 55 they located. We’ve always known this.”

Anthropologists at the University of South Florida exhume a grave at the Arthur G Dozier School for Boys in 2013. Photograph: Edmund D Fountain/AP

A troubled history

The Florida School for Boys was intended to be a model for juvenile justice when it opened in 1900, its first students, mostly black and aged eight to 21, guilty of only minor offences such as larceny or running away from home. Others were youths declared “incorrigible” by their families, or orphans with nowhere else to go.

The stated intention was to restore them to society as rehabilitated young adults. But the facility quickly ran into controversy. In 1903 an inspection found children restrained in leg irons. In 1914, a mystery dormitory fire killed six children and two staff members who were buried in the school cemetery that students christened Boot Hill. In 1918, 11 more fell victim to a flu outbreak.

Dozens more are thought to have died there, the most recent only 28 years before the school closed in 2011. Official records, poorly maintained and incomplete, indicated 31 burials from 1914 to 1973, mostly the result of illnesses or drownings. But USF researchers partnered with local and state law enforcement and the University of North Texas science centre set the figure at a minimum of 98.

Worse was the way in which some had died, forensic results revealing shotgun pellets, blunt force traumas and “substantial evidence” of malnutrition and infections. The testimony of hundreds of survivors in a state-ordered investigation earlier this decade painted a picture of a grisly reign of terror in which even trivial transgressions such as smoking drew vicious beatings with a leather and metal belt.

Former students said they feared most the White House, where boys were chained to tables or walls and flogged into unconsciousness, some never to return. There were allegations of a secret “rape dungeon” in the cellar of the dining hall.

White metal crosses mark graves at the cemetery. Photograph: Michael Spooneybarger/Reuters

One survivor, Dick Colon, said he had witnessed a boy tumbling in an industrial clothes dryer and his body later removed, wrapped in linen. According to the Bones of Marianna, a 2013 account of the Dozier story, another survivor, Roger Kiser, recalled a similar scene and a laundry room supervisor telling him “Another one of you little bastards just bit the dust” as a stretcher was carried out.

Kiser, now 73, claims to have witnessed a second murder, a boy beaten and left to die in a bathtub. Such stories, Cooper said, help explain why so many survivors struggled to adjust after release, battling alcoholism or other substance abuse.

“A lot of them ended up in prison,” he said. “I mean, what do you expect? They literally turned monsters loose, monsters that they created.

“This should have never happened to any of us. Most of us have paid the price for what happened to us as children and gone through life with serious problems. You can’t just forget about it, it haunts you, it ruins you. I still have issues, I’m not going to lie to you. I have a temper that’s about two inches long.”

‘The end of a long, hard journey’

Still, Cooper says he was one of the lucky ones, completing a successful career in the military, now president of the White House Boys, one of a number of support groups totalling several hundred members whose refusal to keep quiet forced Florida’s political leaders to take action.

Ultimately, an investigation by the Florida department of law enforcement ordered by then governor Charlie Crist in 2008 found insufficient evidence to prove or refute physical or sexual abuse, and prosecutors declined to charge the few former staff members still alive.

Ovell Krell, sister of George Owen Smith, the first victim positively identified from one of the 55 unmarked graves speaks during a news conference on 7 August 2014, at the University of South Florida in Tampa, Florida. Photograph: Chris O’Meara/AP

But the appetite for answers led to the state calling on USF’s forensic pathology team, which used ground-penetrating radar to locate 55 graves, all but 13 in unmarked plots outside Boot Hill. From exhumations that began in 2013, researchers made 15 presumptive DNA matches and seven positive, among them George Owen Smith, whom authorities claimed ran away after his family reported him missing in 1940. Ovell Krell, his sister, told the Guardian in 2014 the identification marked “the end of a long, hard journey”.

Erin Kimmerle, USF associate professor of forensic anthropology and lead researcher, said: “A big step in any historic case like this is acknowledgement, recognising what happened to the different people, the victims, the families, the stakeholders, and trying to bring out the facts and the truth.

“That in itself is a type of justice. It’s still critical for anyone who’s been personally affected to have that knowledge because until then you can’t begin to mourn, heal or move on.”

Kimmerle continues to work with law enforcement and genealogists to try to identify remains, and is waiting to hear if her team will be called on again following the discovery of 27 “anomalies consistent with possible graves” by a contractor working to clean up the site.

Ron DeSantis, the Florida governor, has asked Jackson County commissioners to work with state agencies to devise a path forward, highlighting the “utmost sensitivity” of the issue.

Cooper said he was confident DeSantis would do the right thing, following the state’s official 2017 apology for “the history of physical, mental and sexual abuse” committed by Dozier staff and agreement to allow remains recovered there to be re-interred last month in a memorial ceremony at a Tallahassee cemetery.

“Every child that’s buried on that property should be located,” Cooper said. “I don’t want to see as they go on and clean up and construct stuff, ‘Well we found 10 more here, we found six more there, we found four over here.’

“It’s time to get it over with.”