BOISE, Idaho — Glenn Cox went before the parole board with a plan and a bandage on his forehead.

He had already been accepted into a live-in substance abuse treatment center. For the first time in a long time, he was hopeful about the future.

And the bandage? He’d slipped on a freshly mopped prison bathroom floor, he told parole commissioners. No big deal.

After reviewing his case, including his criminal history of 12 drunken driving arrests, the board sent him back to prison with a tentative parole date two years out.

Five days later, Cox was dead.

Prison workers found him in his cell: He was stabbed in the neck with a pencil, beaten with a cane and strangled, according to Idaho Department of Correction records obtained by The Associated Press. His cellmate — a triple murderer — is the only suspect.

Cox’s death highlights the difficulties faced by prison officials across the U.S. in determining housing assignments for an ever-evolving population of inmates.

“I get it when people say, ‘Man, how can a DUI inmate live with a convicted murderer?’” Corrections Director Henry Atencio said. “On the surface you wonder — like, ‘Yeah, that’s kind of weird.’”

Actually, the drunken driver and the triple murderer were only a few points apart on their risk assessment score, a complex number system Idaho and other states use to classify prisoners as minimum-, medium- or maximum-security risks. The system scores inmates in categories such as the crimes they committed, how long they’ve been behind bars and whether they’ve broken any prison rules.

Sometimes, however, the numbers lie.

SUFFERING FROM HIS MISTAKES

Cox was a longtime alcoholic and had tried and failed to quit drinking before, said attorney John Stosich, a family friend who represented Cox in some of his legal proceedings. But he also was recently diagnosed with a mental illness, and believed treating the illness and alcoholism simultaneously was the key to staying sober.

“Glenn suffered from his own mistakes and understood the consequences were related to his own decisions,” Stosich said after Cox’s September death. “But he also realized, maybe for the first time, he could change his decision making and improve his future.”

Cox began his latest prison stint in 2015, after police caught him trying to get a friend’s vehicle out of a privately owned field, where it was stuck. That was both a probation violation — he wasn’t allowed to drive because of a previous drunken driving conviction — and a new crime, because he was drunk.

“We did a plea agreement for Glenn, and he went to jail and never bonded out,” Stosich recounted.

Cox was designated a minimum-security offender but was sent to the Idaho State Correctional Institution south of Boise — a medium-security facility — to wait for a minimum-security bed to open up. Idaho’s 10 prisons have been filled to capacity since last year, holding about 8,300 inmates.

The state routinely has about 900 more minimum-security inmates than it has beds.

Prison officials try to manage the shuffle the best they can, an effort Idaho State Correctional Institution Warden Keith Yordy says is like assembling a new 1,000-piece puzzle every day.

“One day there’s 1,100 pieces in the box. The next day there’s 900 pieces in the box. And they don’t always fit,” he said. “At my facility, we do 15,000 moves a year — and that’s a conservative estimate.”

CELLMATE’S HEINOUS CRIMES

James Junior Nice was moved from another Idaho prison to the cell he shared with Cox on July 23.

He was 12 years into his life-without-parole sentence and had only four relatively minor rule violations on his prison record. He even had a prison job as a “companion inmate,” helping monitor prisoners on suicide watch.

“Those are inmates who are well-behaved, for the most part. They covet that position,” Atencio said.

In fact, Nice was at the low end of medium in Idaho’s security rating system. He will never reach the minimum security rating because of the horrific nature of his crimes: Nice poisoned his three young children to death, murders a judge said he committed, in part, out of vindictiveness toward his ex-wife.

Deputies found Nice and the bodies of his twin 6-year-old boys and 2-year-old daughter four days before Christmas in 2005. The children were killed with rat poison and over-the-counter medication; authorities said Nice also tried to poison himself but survived.

He was sentenced to three consecutive life sentences without the chance of parole. The judge cried.

A PORTENT OF TROUBLE?

The day before Cox’s parole hearing, a prison staffer noticed his head injury. Cox told her the same thing he later told the parole board: He’d slipped on the wet floor.

He never mentioned his cellmate, but the staffer worried Cox was assaulted and reported her concerns to the head of the cellblock, according to interviews and documents obtained by the AP from the parole board and Correction Department through a public record requests.

The wound was never formally documented, department investigators said. The agency is investigating, though whether Nice caused the injury may never been known.

Some experts say prison confrontations are inevitable, especially when medium- and minimum-security prisoners are housed together.

“Look, 70 percent of people in prison are in for violent offenses, so the likelihood of something happening is of course going to increase,” said Dan Pacholke, a corrections consultant and prison safety expert. “The question is, are you doing all the things you can to mitigate or reduce that kind of behavior?”

Pacholke advocates placing minimum-security offenders in “discrete housing units” within medium-security prisons.

“Because mentally, they’re all gearing up for release,” he said. “They’re all kind of moving in the same direction.”

The same can be done for units made of military veterans who struggle with loud noises or have other PTSD symptoms, or inmates 65 and older, who might prefer earlier bedtimes and quieter shared areas, Pacholke said.

ONE SUSPECT, NO ARRESTS

Five months after Cox’s death , the homicide investigation also continues.

Only two people were in the room when Cox died in the wee hours of Sept. 22. By that afternoon, the county coroner confirmed Cox died of injuries related to an assault.

The Ada County Sheriff’s Office confirmed Nice is the only suspect, but no charges have been filed.

Nice is already serving a life sentence and has since been moved to a maximum-security cell. His previous court records are sealed, and since he has not been charged, he has not been assigned an attorney in Cox’s death. The AP attempted to reach Nice for comment, but prison officials declined to forward emails and said he wasn’t receiving mail. Nice was not reachable by phone.

“The No. 1 thing is the public is safe from him. He is in custody,” sheriff’s spokesman Patrick Orr said. “These types of cases demand a thorough investigation. That can take a long time.”

Ryan Labrecque, a Portland State University assistant professor and former correctional officer, noted a lot can be learned when inmate housing decisions end in adverse outcomes. His research examines how prison management, personality factors and even the physical condition of prison facilities can impact inmate behavior.

In most states, inmate classification is based on “static” factors such as behavior and criminal history, he said. But emerging practice shows there are also many “dynamic” factors, such as inmates’ attitudes, associates and work experience.

“Across the board, institutions focus a little too much on the static factors, when focusing on these criminogenic needs is the way to go,” he said. “It’s a science but also a little bit of an art, and we can never stop learning on how we improve how we place offenders.”