The fact that Ms. Guyger was not immediately arrested, and was initially charged with manslaughter, helped spark protests in the days after the shooting.

“This case exposed what’s wrong about how the department handles police shootings,” said Changa Higgins, the head of the Dallas Community Police Oversight Coalition. “It does represent a big shift in the idea of how we hold officers accountable when they murder.”

The trial unfolded in a diverse city — Dallas is 42 percent Hispanic, 29 percent non-Hispanic white and 24 percent black — that notably has people of color in nearly all of the major leadership positions. The mayor of Dallas, the police chief and the Dallas County district attorney are all black, as is the judge who presided over this case. Of the 12 jurors and four alternates, seven are African-American, four appear to be white and five are of other races and ethnicities.

“People in Dallas County worked hard to create an environment where justice is possible,” said S. Lee Merritt , a civil rights lawyer who represents Mr. Jean’s family, contrasting the situation with other cities, like Ferguson, Mo. There, a grand jury made up of nine white people and three black people decided not to indict a white police officer in connection with the 2014 shooting death of an unarmed black teenager, Michael Brown .

Mr. Merritt also represented the family of Antwon Rose II , an unarmed black teenager who was killed while fleeing a traffic stop in East Pittsburgh, Pa., last year. In that case, the white officer was acquitted by a majority-white jury.

“You have a progressive judge, which produced a diverse jury, and a district attorney that ran on a platform of police reform,” Mr. Merritt said. “That’s what’s different.”