The races for Ramsey County attorney and sheriff gained momentum as candidates filed campaign finance reports and a challenger emerged in an otherwise narrow field.

Ramsey County Attorney John Choi announced plans to run for a third term; there are no indications yet that anyone intends to challenge him. Sheriff Jack Serier launched his campaign last year and has at least one challenger — Mike Martin, assistant director of emergency management for the University of Minnesota.

Choi raised $19,280 last year, bringing his total balance to $105,565, according to the county elections office. Serier raised $8,327.

Both were the only candidates in their races to file campaign finance reports, but challengers have several months to make their bid. The filing for candidacy doesn't open until May 22, and it closes June 5.

Choi said his goals include reforming juvenile crime through diversion and treatment programs and improving the rehabilitation of certain offenders, such as low-level drug users. He also said he would continue combating gender-based violence and sex-trafficking.

"I kind of feel like this is my life's work," Choi said.

Trisha Collopy — Star Tribune file, Star Tribune
Ramsey County Sheriff Jack Serier

Choi was the state's first county attorney in modern history to charge a police officer, Jeronimo Yanez, for fatally shooting a civilian, Philando Castile, while on duty. He was criticized at times for not taking quicker action on the case. A jury found Yanez not guilty.

Dianne Binns, president of the St. Paul NAACP, said she supports Choi despite her disappointment in the verdict.

"He did what he was supposed to do," she said. "I think the county attorney was out-lawyered."

Other hurdles Choi faced during his tenure include the revelation in 2012 that the St. Paul police crime lab, which his office relied on, had poorly maintained testing instruments and inappropriately trained staff at the time.

Choi was first elected county attorney in 2010 and won re-election in 2014. He earns $175,214.

Serier, who was appointed by county commissioners last year to replace Matt Bostrom, said in his campaign kickoff that he would invest in community engagement and recruitment. He noted that each new group of correctional officers and deputies was composed of more than 50 percent women and people of color.

Martin, who was a Minneapolis police officer for 23 years, announced last week that he'll run for sheriff.

"We need to be an agency that respects people's rights and civil liberties," Martin said Wednesday.

Martin said his priorities include restoring confidence in the office among the public and rank-and-file, engaging with the community and improving conditions at the jail for workers and inmates.

Attorney and lobbyist Nancy Haas had expressed interest, but said Wednesday that she would not run.

Vadnais Heights Mayor Bob Fletcher, who served as Ramsey County sheriff for 16 years, said he would decide in May whether he'll enter the race. Fletcher has been critical of Serier.

Chao Xiong • 612-270-4708

Twitter: @ChaoStrib