IT SEEMED INEVITABLE that it would emerge one of the main fault lines in the race for Suffolk County district attorney: Kevin Hayden, appointed to the post in January by Gov. Charlie Baker to fill the seat vacated by Rachael Rollins, would trumpet his years of experience as a prosecutor and point to the fact that his rival, Boston City Councilor Ricardo Arroyo, has no prosecutorial background and only a few years under his belt practicing law in any capacity.

What came as a surprise, however, was that Hayden launched the line of attack in response to Arroyo scoring an endorsement from Boston Mayor Michelle Wu. What’s more, after Wu announced her support at a campaign event with Arroyo on Saturday, Hayden’s campaign issued an unusually sharp-edged statement that not only jabbed Arroyo but questioned the judgment of the city’s new mayor as well. 

“If Mayor Wu believes a novice attorney with zero public safety experience should be the top law enforcement officer in the county, that’s her choice. We’re confident voters will disagree,” Hayden campaign spokesman Adam Webster said in a statement. 

On Monday, Wu defended her endorsement during an interview on WBUR’s “Radio Boston.” The talk from Hayden’s campaign about Arroyo’s lack of experience, she said, “is code and signal for upholding the status quo.” 

That status quo, Wu said, “hasn’t been working for everyone, and so we want to see the types of reforms that former district attorney Rollins had put into effect, which have been documented through research and data to bring about outcomes that in fact reduce crime and heal communities and stabilize and reduce recidivism.” 

Wu said Arroyo’s “platform of really reducing crime while healing and providing the resources to build community” is “exactly what we need.” 

Arroyo, who is carving out a path to Hayden’s left in the Democratic primary, has made clear that he aims to continue the reform-minded approach taken by Rollins. That turn away from the tough-on-crime policies of the 1990s was encapsulated most vividly by her default policy of not prosecuting a list of 15 lower-level offenses. 

Arroyo, 34, worked as a public defender for four years before his election to the city council in 2019, but has no background in a DA’s office. Hayden, 53, spent more than a decade in the Suffolk County DA’s office, including helming its Safe Neighborhoods Initiative, which focused on community-based solutions to gang violence. 

Hayden says he has long put into practice some of the reform-focused ideas now gaining attention. Earlier this month, he announced that the DA’s office would direct $400,000 from its asset forfeiture fund to support diversion programs offering treatment, not prosecution, to those suffering from addiction and mental health issues in the troubled Mass. and Cass area of Boston. 

But he and Arroyo differ on some key policies, including the maintenance of a gang database, which Hayden wants to keep and Arroyo says should be dismantled. 

After Wu’s latest comments, Hayden’s campaign doubled down on its questioning of his background – and the mayor’s endorsement. 

“Experience matters,” said Webster. “I doubt Mayor Wu would hire a school superintendent with just four years of experience as an educator or hire a police commissioner with just four years of public safety experience.” 

Boston is in the process of hiring new officials for both of those positions. Webster’s assessment of the kind of credentials Wu will look for in filling the jobs may be on the mark. But the DA’s post is decided by voters, and Arroyo – and Wu – are betting that they’ll be more persuaded by Arroyo’s vows of progressive prosecutorial change than arguments over experience. 

Along with his decidedly progressive platform, Arroyo will be greatly aided by his familiar name in a race against a political unknown. His brother was a Boston city councilor and one-time mayoral candidate, while his father was a city councilor who has gone on to be elected Suffolk register of probate – appearing on the same countywide ballot the DA runs on. 

Arroyo campaign manager Mohammed Missouri, in a statement, called the comments from Hayden’s camp “a desperate attack from an appointed official who is rolling back the progressive reforms that were overwhelmingly voted for when Suffolk County elected Rachael Rollins.” 

While background as a prosecutor has long been considered practically a prerequisite for running for DA, in a sign of how different the times are, Arroyo’s campaign pumped up his work as a public defender in making the case for his election.  

“Councilor Arroyo has represented hundreds of people in his career as a public defender,” Missouri said, “and that experience is what drives his vision for a more just system that reduces crime while addressing rampant disparities.”