Suffolk County Sheriff Steven Tompkins endorsed Boston City Councilor Michelle Wu's bid for mayor Tuesday, adding a prominent Black law enforcement voice to the apparent front-runner's choir of elected supporters.

Pointing to a working relationship forged on the 2012 campaign trail for Massachusetts U.S. Senator Elizabeth Warren, Tompkins called Wu "family," adding he observed her to be a hard worker and good multi-tasker.

"I sat next to Michelle for about four and a half months," he said of the campaign period. "Her portfolio for Senator Warren was huge, but at the same time she was planning her wedding and studying for the bar exam… that's the kind of individual that I invest in," he said, announcing his endorsement outside the Reggie Lewis Center in Roxbury.

Tompkins, who earned about 206,000 votes in Boston in his last election in 2016, told GBH News he had intended to sit out Boston's preliminary cycle until about a week ago. He changed his mind, he said, after a conversation with a friend led him to conclude that he should help his preferred candidate make it past the primary with an endorsement.

Speaking to GBH News, Tompkins said he and Wu are "aligned" when it comes to vocational education, but he declined to comment on Wu's plan for re-shaping the Boston Police Department contract to include a number of progressive reforms.

"She and I will have our conversations about that, but I'm not going to make a comment [on] what she's going to do in that area," he said. "I think it's best for the candidate to talk about that."

Wu, who is Taiwanese-American and enjoys strong support from white progressive voters, has increased her outreach to diverse communities in recent weeks, earning the backing of the Ward 1 Democratic Committee in Boston's heavily Latino East Boston neighborhood.

Tompkins said he expects some criticism for choosing to back Wu over one of the two Black women in the race.

"I probably will get that today," he said, when asked about the disapproval some Black supporters of Wu report enduring. "To me, everything is not just necessarily about race."

"I think that Andrea Campbell and Kim Janey are stellar," he continued. "I think they're serious advocates for doing the right thing for the city of Boston and I've got nothing but the ultimate respect for both of them. But, clearly, this endorsement wasn't about the color of my skin or the candidate's skin."