DONNA PATALANO, who is challenging incumbent Middlesex District Attorney Marian Ryan, looks like exactly the right candidate at the right time.

The Winchester attorney is pushing a strong reform platform focused on addressing racial disparities in the criminal justice system and the need to rethink policies of the tough-on-crime era of the 1980s and 90s. It should be a particularly appealing message in the liberal-leaning county, and it comes amidst a reform wave that has states and communities across the country looking to new approaches that can protect public safety while lowering incarceration rates.

The biggest challenge for Patalano’s reform message? She’s up against a sitting district attorney who has positioned herself as a progressive leader on those very issues, someone who has bucked her fellow DAs by embracing reforms that they opposed.

The result is a lively Democratic primary face-off for an important office, but one that lacks some of the sharp contrasts that let voters draw clear distinctions between candidates, a dynamic that will probably play to Ryan’s advantage.

“I am, in this race, the proven progressive,” Ryan said at a debate between the two candidates last week in Arlington, where she seemed determined to showcase her reform credentials before a decidedly liberal crowd at the Unitarian Universalist Church.

Ryan pointed to her status as the only one of the state’s 11 DAs not to sign on to a 2015 letter to the editor to the Globe defending mandatory minimum sentences. She also highlighted her subsequent support for the more sweeping Senate version of a criminal justice reform bill, a position that put her at odds with 9 of her 10 colleagues who coauthored a letter to legislative leaders that was sharply critical of the bill.

She has also been a strong advocate of “restorative justice,” an approach that focuses on repairing communities by bringing together crime victims and perpetrators.

“I have taken the hard stands. I have stood apart from the other district attorneys,” Ryan, a Belmont resident, said of her tenure overseeing prosecutions across the county’s 54 cities and towns.

What Ryan calls the record of a “proven progressive,” however, Patalano calls the moves of a savvy operator who is adapting to the changing political winds.

“She’s definitely moving to the left after she was challenged by me, but that kind of lip service isn’t enough,” said Patalano, who pointed to Ryan’s move in January to end the practice of asking for cash bail in routine cases involving low-level offenses. “We need a different perspective. My opponent has been a prosecutor since Jimmy Carter was president.”

Ryan is a career prosecutor who joined the Middlesex DA’s office in 1979 and has directed several units there during that time.

Patalano has had a more varied career. She worked in health care management before going to law school while in her 30s. She has served as a defense lawyer, chaired the state board of bar overseers, which monitors the conduct of lawyers, and worked in the Suffolk County DA’s office, where she developed the office’s first conviction integrity unit that reviews possible wrongful convictions.

Patalano said a central challenge for the DA’s office is addressing the fact that the “criminal justice system treats different people differently.” She said blacks are incarcerated at eight times the rate of whites. “If that’s the end result of our criminal justice system, something’s going wrong in the courtroom,” said Patalano.

But she said the DA’s office lacks the data to look more closely at each step in the system to identify where disparate treatment of defendants may be occurring.

Ryan said she accepts that there are disparities and says what’s most important are the steps being taken to deal with them. She pointed to her move to end the use of cash bail for low-level crimes and increases in the county’s use of court diversion programs that steer less serious cases out of the criminal justice system.

Patalano argues that increased use of diversion alone is not proof that disparities are being addressed without demographic data on who is being offering diversion and which courts across the sprawling county of 1.4 million residents are using it and which are not. “Who gets diverted? Who gets to go to drug court? Who gets pretrial probation? We don’t know any of this,” said Patalano. “Our justice system is the moral backbone of our government. And if it functions like a black hole, then how can we know what we’re doing is fair and just?”

The state courts and DAs offices are notorious for their antiquated record and data systems. Millions of dollars have been pumped into updating their information systems, but there remain big gaps in the kind of data that are available on what takes place in courts.

Ryan said it’s estimated that it would $16 million statewide to upgrade those systems and link data across all the state’s counties. In the meantime, she said she is partnering with researchers at Northeastern University and the American Institutes for Research who are building databases to look at practices and patterns in Middlesex County cases.

Despite Ryan’s claim to be reducing the use of cash bail to hold defendants before trial, data from the Vera Institute of Justice, a New York-based research and policy center, show that pretrial detention of defendants in Middlesex has more than doubled since 2013, the year she took office.

Ryan said it was hard to know what explains the increase, citing the fact that federal detainees are also held in county facilities and not accounted for separately in the figures.

Patalano offers one possible explanation.

“I draw the inference that a lot of it is her knee-jerk reaction after the Jared Remy case, where she removed discretion from district court prosecutors and required them to no longer ask for bail in domestic violence cases,” said Patalano. “Nobody wants a tragedy, but locking everybody up is not making anybody safer.”

In the 2013 case, the son of Red Sox announcer Jerry Remy, who had a long record of domestic violence, was charged with murdering his girlfriend, Jennifer Martel, one day after Middlesex prosecutors agreed to his release following his arrest for allegedly assaulting her.

Ryan was appointed to the DA’s post four months before the Martel murder by then-Gov. Deval Patrick when her predecessor, Gerard Leone, resigned to take a private-sector job.

Ryan has been dogged since early in her tenure by questions about her management and decisions in several high-profile cases.

The Remy case prompted an outside review, which faulted the office’s handling of the matter. But Ryan got caught up in further controversy when it was reported that she withheld 19 pages of the review focused on interviews with prosecutors and advocates involved in the case. Because the version of the report Ryan initially released did not include the report’s table of contents, it wasn’t possible to know there were sections omitted, the Globe reported in 2014 when the issue surfaced.

Ryan released the additional pages only after the Globe received a tip that there was more to the report and made a public information request for the missing pages. Ryan said she had held the pages back to protect employees, whom she encouraged to speak candidly to investigators.

Ryan also came in for harsh criticism in the case of Irish nanny Aisling Brady McCarthy, who was charged with the 2013 killing of 1-year-old Rehma Sabir. In 2015, a judge upbraided the DA’s office for not turning over to defense lawyers for more than a year notes from prosecutors’ consultations with an eye specialist who cast doubt on whether injuries to Rehma Sabir’s eyes were the result of abuse.

Prosecutors are obligated to turn over to defense lawyers any potentially exculpatory evidence they gather. Melinda Thompson, a former Middlesex assistant district attorney who served as one of McCarthy’s defense lawyers, said it was shocking to see such blatant disregard for those rules.

“You’re not just there to win and put everyone in jail who gets arrested,” she said of the prosecutor’s role. “That seems to be the goal now – to sort of hide the ball and make sure somebody is convicted,” said Thompson, who says she’s is troubled by the office’s leadership under Ryan.

“I think it’s extremely concerning,” said Patalano. “To me it is indicative of the culture that my opponent presides over, and that is one to get a conviction at any cost rather than to work in the interest of justice. It certainly doesn’t square with the idea of being a progressive.”

Ryan acknowledges that the office erred and should have provided the notes from the conversations with the eye doctor sooner. But she rejects the idea that it reflects a pattern in her office. “As with any industry or business, can you find examples where something didn’t go perfectly? Of course you can,” said Ryan. “That is not the legacy of Middlesex County.”

The charges against McCarthy, who was held without bail for more than two years, were ultimately dropped.

Ryan says voters should consider the broader context of her office’s record and her own recognition, including the fact that she was recently named co-chair, along with Attorney General Maura Healey, of a Massachusetts Bar Association working group on conviction integrity and enjoys the support of leaders of the state’s criminal justice reform efforts such as Sen. Will Brownsberger.

“Marian really has been a leader for reform among the DAs,” said Brownsberger, cochair of the Legislature’s Joint Committee on the Judiciary and lead sponsor of the sweeping criminal justice bill passed earlier this year. “She’s been a very constructive voice trying to move forward an approach that lifts people up instead of locking them up to whatever degree we can.”

Tom Reilly, a former Middlesex DA who went on to serve as Massachusetts attorney general, also praises her support for the bill. “I’ve been impressed with Marian’s broader vision for the office. I was impressed with the fact that she broke ranks with most of the district attorneys through the state,” said Reilly, who is supporting Ryan “wholeheartedly.”

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