The probe will broadly focus on whether the Mississippi Department of Corrections adequately protects prisoners from violence at one privately run and three state-run facilities, including the Mississippi State Penitentiary. The facility, at Parchman, will undergo further investigation into its handling of suicide prevention, mental-health care and solitary confinement.

On Thursday, advocates of families whose relatives are incarcerated in the MDOC were hopeful but said a probe was long overdue.

“These issues [have] been raised in the past not only by members of our organization, but also by dozens of other advocacy groups and individuals,” Jennifer Davis, a member of Mississippi Dreams Prisoner Advocacy, said on behalf of the group in an email to The Washington Post.

Mississippi Gov. Tate Reeves (R), who last week pledged reforms to the state prisons, welcomed the investigation. Reeves offered the state’s cooperation with federal officials to “right this ship.”

The investigation represents “a hugely important development” for the division, according to Vanita Gupta, who headed the Justice Department’s Civil Rights Division under President Barack Obama.

Gupta, who now oversees the Leadership Conference on Civil and Human Rights cited a combination of factors that probably paved the way for the Trump administration to open the investigation, including national media attention, the high death toll and acknowledgment from state officials that the system was in crisis.

“The opening is important,” Gupta told The Post. “But how the investigation is allowed to proceed and once findings are made, what are the tools to properly address these problems? That very much remains an open question.”

As one of his last acts in office, former U.S. attorney general Jeff Sessions issued a memo in late 2018 that restricted police reform agreements and limited the timeline for consent decrees, with some rare exceptions, to no more than three years.

Consent decrees are binding settlements between the federal government and a state or municipal body, like a corrections department. They are the most effective tool the federal government has to enforce reform, according to Jonathan Smith, the former chief of the special litigation section of the Justice Department’s Civil Rights Division until 2015. Smith was skeptical that any eventual consent decree with a three-year “sunset” would be adequate.

“You look at the Mississippi prison system issues — they’ve been going on for 50 years,” Smith told The Post. “They’re deep, systemic and will take a long time to fix properly.”

Mississippi’s prisons have long faced complaints that inmates are forced to live in squalid conditions, lack adequate mental-health care and face violence from staff — and the prisoners they allegedly deputize.

Harsh prison conditions are a century-old legacy of Mississippi’s penal system, said David Oshinsky, who chronicled the brutal history of Parchman in the 1996 book “Worse Than Slavery: Parchman Farm and the Ordeal of Jim Crow Justice.”

“In terms of violence, money spent and real supervision, Parchman had none of it,” Oshinsky told The Post. An inmate’s death at Parchman in late December sparked a prison riot that led to three more deaths and days of lockdown.

“The real difference today from 100 years ago is that Parchman in 1920 was a real moneymaking operation for the state,” Oshinsky said. The state once profited from prison slavery in a practice euphemistically known as “convict leasing.”

With one of the highest incarceration rates in the country, Mississippi prisons have struggled with a lack of funding, overcrowding and understaffing, which at times has led to visitor lockdowns that last months. Even a 2014 prison reform law did little to offset the problems. A 2019 investigation by ProPublica and the Mississippi Center for Investigative Reporting found that long-standing problems of violence, gangs and unsanitary conditions were worse than ever.

Gupta acknowledged the common fear that prison-condition investigations will lead to states being asked to spend more money on their corrections facilities. The response often means new prisons or bringing in private prison operators, she said. Gupta noted other solutions can take the shape of criminal justice and sentencing reform “to stop the flow of people into prisons to begin with” — alternatives that have growing bipartisan support.