In preparation for taking the bench as a newly appointed federal judge in 1994, Mark W. Bennett visited a federal penitentiary in Atlanta.

It was, he says, the scariest experience of his life. But by the time he retired this past March as U.S District Court judge for the Northern District of Iowa, based in Sioux City, the 69-year-old Bennett had deliberately paid visits to 16 federal prisons, one of those at least 10 times.

It first happened in 2004, when the judge, who was nominated by President Bill Clinton, was attending a conference in Long Beach, Calif. That was just after he had sentenced four drug dealers from South Central Los Angeles for robbing a Sioux City bank — twice.

They were convicted, and Bennett sentenced them to Terminal Island men’s prison in California. Since he was out there, he decided to visit and was given a tour. Though not ready to be reunited with the four, “It dawned on me I would learn a lot more if I just talked to inmates.”

So he requested that, and had a 90-minute meeting with three convicts he described as “rough looking” men. He said one broke into sobs, saying he could never have imagined a federal judge caring about his opinion.

“It just kept gnawing at me,” Bennett said. “An inner voice said, ‘Next time, I will interview people I’ve sentenced.’ ” So began an extraordinary journey of seeking out people he had confined to see how they were doing.

In 24 years on the bench, Bennett sentenced 4,000 people. And in 15 of those years, he visited 400 of them in prison. He says 95 percent responded positively.

“Mostly I asked, did they feel treated fairly, and (satisfied with) the quality of their court-appointed lawyers,” said Bennett in a recent interview in his office at Drake Law School in Des Moines.

Today he teaches law and heads Drake’s Institute for Justice Reform & Innovation, which does research and training on implicit bias, among other things. He said the vast majority of inmates did, though about a fifth complained about their defense counsel and a fifth said the judge had been too harsh.

That, contends Bennett, is largely due to mandatory minimum sentences stipulated by federal law in drug cases. Nearly half of the inmates in federal prisons are there for drug offenses.

When he had no say in the sentence, Bennett tried to at least get the offenders into prisons with programs they could benefit from. He suggested a culinary arts program at the Federal Correctional Institute in Oxford, Wisc., to an offender who had worked at restaurants.

When Bennett visited the inmate around 2011, close to his release date, he was excited about upcoming interviews with Chicago restaurants. He told Bennett he had saved his life by helping him get on the right track.

The inmate also told him he was the only visitor he ever had in prison.

When he visited another inmate he had sentenced to the mandatory 10-year minimum, a recovering crack addict in her early 20s, she asked Bennett to attend a drug treatment class with her. He did, and told her he was proud of her.

Bennett used other tools to challenge an inherently discriminatory system.

In 2014 he co-authored a piece for a social justice journal with former federal prosecutor Mark Osler. It cited the war on drugs as a major reason that the U.S., with less than 5 percent of the world’s population, has nearly 25 percent of the world’s incarcerated.

“Prison populations have mushroomed through incarceration of increasing numbers of young males, especially young black men, mostly from impoverished urban areas,” it said.

One discriminatory aspect of the law he lobbied against was its differential treatment of powder and crack cocaine. A 1986 federal law created a 100-1 ratio between the amount of powder cocaine and crack cocaine that would trigger a mandatory minimum sentence. Crack cocaine is cheaper and used more by black people, while wealthier suburban white people tend to use powder cocaine.

Under the guidelines, someone convicted of dealing 5 grams of crack could get a five-year sentence, while someone dealing powder cocaine would have to deal 500 grams to get the same sentence.

So in 2009, citing a U.S. Supreme Court directive that judges had the right to disagree with federal sentencing guidelines, Bennett deviated from them and challenged that discrepancy. The U.S. Supreme Court ruled in Bennett’s favor in the case, Spears v. United States.

It’s regrettable that more judges haven’t followed his lead in meeting the inmates they sentenced. But amid the demonization of poor and marginalized people from up high, and the self-serving rhetoric from political campaigns, it is deeply nourishing to see someone at Bennett’s level think independently and speak truth to power with no dog in the race — only an abiding passion for equal justice.

Rekha Basu is a columnist for the Des Moines Register.