Russell Tinsley had a long history of committing serious crimes, including rape and assault with a deadly weapon, in other states by the time he was imprisoned for car theft in New Jersey in 2008.

After each of the prior convictions, in California and Pennsylvania, Mr. Tinsley had followed the conventional path through the American criminal justice system, serving his time and then going free.

But when his two-year sentence was up in New Jersey, officials in the state attorney general’s office petitioned to have him confined for more time under a state law that allows for the civil commitment of dangerous sex offenders — even though he had never been convicted of a sex crime in that state. That was in 2010.

Two doctors who never interviewed him concluded that he lacked skills to function safely in the community and that he should be locked in the state’s Special Treatment Unit until he was rehabilitated.

Over the next 15 years, Mr. Tinsley’s treatment was overseen by doctors who repeatedly failed to show that he had an uncontrollable “mental abnormality,” as required by law, and his care proceeded at a glacial pace, advancing him no closer to freedom, a judge would eventually rule. Still he remains in the unit today, having turned 70 in March.

“I think they want to keep me here until I die,” he said in a recent interview.

Operated in 20 states, programs like the one that has held Mr. Tinsley occupy a fraught and contentious corner of the nation’s criminal justice system, allowing for some sex offenders to be civilly committed to secure facilities even after they have served their full criminal sentences.

Proponents of the programs — who first created them in response to sensational crimes committed by sex offenders who had been released from prison — have said they are needed to keep the public safe. Legal critics, however, have singled them out as violating bedrock principles of due process.

The programs are supposed to provide treatment to offenders and then free them when they no longer pose a threat to the public, and some appear to have achieved that goal. New Jersey’s program, however, has proved one of the least effective at rehabilitating and releasing its residents.

Bradford Bury, a former New Jersey State Superior Court judge who once oversaw the program, said it held some sex offenders to a standard that no other criminals had to meet, not even those convicted of horrifying crimes.

“We let people who intentionally murder a child out on parole,” said Judge Bury, who retired in 2023. “There’s a total inconsistency of the application of the rules, common sense and fairness.”

He added that, by his estimation, one in three of the nearly 400 people now being held in the state’s treatment unit could be freed without any harm to the community.

Interviews with more than 30 current and former employees of the New Jersey center and a review of more than 1,000 pages of court documents and other records reveal a dysfunctional system that fails to achieve its stated aims.

The state evaluates people for commitment based on unscientific criteria, and the evaluations themselves occur with almost no transparency.

And unlike other states, New Jersey requires no trial before ordering someone held in civil commitment — only a petition from the attorney general’s office and the consent of a judge.

Among the people who have been confined to the Special Treatment Unit is a man who was wrongfully imprisoned for a rape he never committed.

Over the past 25 years, the center has conditionally released 253 people, requiring them to comply with strict conditions such as polygraph examinations and random check-ins. They can be returned at any time, however, even for minor offenses. One man was sent back to the unit in 2020 for smoking marijuana, and has been held there ever since.

Of the 750 people who have been committed since the unit’s creation in 1999, just 57 have been fully discharged.

Nine residents have been confined there since the center opened.

Records show that detainees who enter the unit are almost twice as likely to die in custody as to be fully released, leading current and former detainees to mordantly refer to it as a “pine box program.” The best chance of getting out, they say, is in a coffin.

There is also evidence of racial prejudice. A 2020 report by researchers at the University of California, Los Angeles, found that Black people were five times as likely to be held in the New Jersey program as white people, the starkest racial disparity of any such treatment program in the nation.

One of the report’s authors noted that people had to be deemed a risk to society before they were confined to the unit and that research had shown that Black men were more likely to be perceived as dangerous.

Representatives of the New Jersey attorney general’s office declined to comment for this article.

A representative of the New Jersey Corrections Department said that the agency was “committed to the safety, dignity and rehabilitation of all incarcerated individuals,” including residents of the Special Treatment Unit.

One researcher, Cynthia Calkins, a psychologist at John Jay College of Criminal Justice who co-wrote a paper on the unit, said that it seemed to accomplish little despite its cost.

“We spend a lot of resources,” she said, “and the overall benefit appears to be very small.”

Committed, Then Exonerated

In 1996, Rodney Roberts was working two jobs, one as a paralegal and another as a salesman in a men’s store, and living in a Montclair, N.J., apartment with his young son, when a teenager was sexually assaulted in Newark.

Seventeen days later, officers with the East Orange Police Department arrested Mr. Roberts, who, as a younger man, had been convicted of conspiracy to commit rape.

They held him for a more than a month after investigators with the Newark Police Department added his mug shot to a lineup and asked the teenager whether she recognized any of the men as her attacker. She picked Mr. Roberts out of the lineup, they said.

Prosecutors charged him with rape and kidnapping. His public defender advised him to plead guilty to kidnapping, saying he would serve less prison time than if he went to trial for both crimes and was found guilty. Mr. Roberts followed the advice, and the sex assault charge was dropped. He received seven years in prison.

Still, when asked, he maintained his innocence, and the parole board denied him early release in 1998, 2000 and 2003, saying he refused to take responsibility for the crime.

By 2004, he was about to be reunited with his family when the attorney general’s office petitioned to have him committed to the Special Treatment Unit. Records show that the doctor who evaluated him determined that he did not have any particular urge to commit sexual assault. But the doctor recommended him for the unit anyway, saying he was likely to reoffend because of his arrogance and refusal to accept responsibility for his crime.

Mr. Roberts spent the next 10 years at the center, receiving no treatment, he said. Still, once a year, a panel evaluated him and ruled that he was too dangerous to go free.

Then a DNA test of evidence in his case showed that Mr. Roberts had never committed the rape in the first place. In 2014, New Jersey set aside the finding that he was a sexually violent predator and released him from the unit.

Mr. Roberts sued the state the following year for the wrongful conviction and commitment. More than a decade later, his case is still pending.

The same deficiencies that led to Mr. Roberts’s commitment have persisted, current and former staff members of the unit said.

In 2022, doctors working for the state acknowledged in court that making determinations about who was “highly likely to reoffend” defied mathematical precision.

The New Jersey chapter of the American Civil Liberties Union filed papers the next year saying that the admission demonstrated the arbitrariness but also the unconstitutionality of civil commitment.

“If ‘highly likely’ has no replicable meaning or measure or fixed floor,” wrote Liza Weisberg, the A.C.L.U. lawyer who filed the brief, “this means that the statute that you used to civilly commit people and keep them civilly committed is without constitutional guardrails.”

The brief was only the latest alarm raised about the program in the courts.

In 2001, a group of the unit’s residents filed a class-action lawsuit against the center, accusing it of failing to provide the minimum treatment for them to be released. The case led to a period of oversight by a federal monitor who was supposed to ensure that the program improved.

“The monitoring process gave a lot of deference to the prison and, I’m sorry to say to you, to the treatment unit,” says Jenny-Brooke Condon, a law professor at Seton Hall University who helped the residents with the original lawsuit.

Since then, she added, “My fear is that things have probably gotten worse.”

A Sense of Hopelessness

Inside the Special Treatment Unit, the prevailing sense among the residents has been one of hopelessness.

The center’s operators have told them that the key to getting out is progressing through phases of treatment. But in practice, as the federal monitor noted, the program can make doing so difficult, if not impossible.

In one report, the monitor noted that the program was advancing residents through treatment even more slowly than it had before the federal oversight began. In another, the monitor said that the program appeared not to be following its own guidelines by holding residents in some treatment phases for three to four times longer than they were supposed to be.

Interviews and records revealed other problems. Some employees counted by the unit as “psychologists” did not meet state requirements to be classified as such — or even as licensed therapists outside of the building.

The employees have some clinical experience but might never have run group treatments, said one current unit therapist, who spoke on the condition of anonymity because they were not authorized to discuss the program.

Many of the employees have never worked with offenders before and, although they are well intentioned, they often appear to be overwhelmed and even terrified, the therapist said.

And the treatment they are in charge of administering is questionable at best, residents and former employees said.

“They did a treatment program that was never validated — somebody made it up,” said Dr. Vivian Shnaidman, a psychiatrist who worked at the center for three years in the mid-2000s. “There was no research to back it. And they just made everybody do these specific things that they invented.”

Heather Ellis Cucolo, an adjunct professor at New York Law School focused on sex offender law, said treatment in New Jersey’s program is offered only sporadically.

“Treatment is used as a way to keep persons longer than what may otherwise be constitutionally appropriate, and treatment has not been shown to be effective by any real criteria in reducing risk,” said Ms. Cucolo, a former public defender who worked with the center’s residents. “It’s just a way to keep these people indefinitely.”

When not in treatment, residents spend their days in run-down quarters on the campus of a state prison that has at times been overrun by rats, bed bugs and mold, interviews and records show. The heating system has failed in the winter and the air-conditioning has stopped working in the summer.

(The representative of New Jersey’s Corrections Department said that all of the agency’s facilities received “comprehensive, regular pest prevention and mitigation.”)

It’s not unusual for residents to undergo arbitrary strip searches or worse at the hands of guards, records and interviews show. In December 2024, a guard pleaded guilty to aggravated assault after beating a resident in the unit who died of a stroke days later.

After spending 19 years in the Special Treatment Unit, Najeev Mohammed has “given up” and accepted that he will never go free, he said in an interview.

“It’s a never-ending situation,” he said. “It just keeps going, going, going, going — that’s it, until you become like a mummy.”