The video opens with blood already soaking through the driver’s shirt, and the police officer who shot him cursing, his gun still pointed at the dying man.

The driver’s girlfriend — who watched the fatal encounter and streamed the gruesome aftermath in live video to Facebook on Wednesday night from the passenger seat — asks at one point for help.

Her plea brought scores to the street within hours in an angry protest that rolled through the day at the governor’s mansion here and across the country, echoed in a congressional hearing with the FBI director and brought a grim-faced President Obama to the podium in Poland to call for greater urgency in police reform.

In Dallas, a downtown protest march in the evening turned violent, when two snipers shot 11 police officers, leaving four of them dead, the city’s police chief said.

“This is not just a black issue. This is not just a Hispanic issue. This is an American issue,” Obama said. The fatal police shootings are “symptomatic of a broader set of racial disparities that exist in our criminal justice system.”

Protesters are taking to the streets around the country after two black men, Alton Sterling of Baton Rouge and Philando Castile of St. Paul, Minn., were fatally shot by police within 48 hours of each other. (Victoria Walker,Gillian Brockell/The Washington Post)

In the wake of this latest in a long string of police shootings — and less than 48 hours after another black man was killed by police in Baton Rouge — Minnesota authorities voiced shock and sympathy and vowed justice.

“Nobody should be shot and killed in Minnesota for a taillight being out of function,” said Gov. Mark Dayton (D). “Would this have happened if those passengers would have been white? I don’t think it would have.”

Earlier, in front of protesters at the governor’s mansion, Dayton had tried to console relatives of the driver, Philando Castile, 32, who died Wednesday night at a Minneapolis hospital. “I can’t tell you how sorry I am that this terrible tragedy was forced upon your family,” he said.

“I don’t want you guys to say you’re sorry!” shot back Castile’s girlfriend, Diamond Reynolds, her retort echoed by the surrounding crowd. “I want justice.”

Their terse and public exchange, captured on national television, encapsulated the frustrations of African Americans in the community here and across the nation. Through the night, demonstrators rallied against police brutality, in front of the White House and in New York’s Times Square, where police made several arrests. Protesters marched in Chicago, Philadelphia, Atlanta and Los Angeles.

In Dallas, gunfire broke out around 8:45 p.m. while hundreds of people were gathered to protest the fatal police shootings this week. Police Chief David O. Brown said two snipers shot 11 police officers from elevated positions during the protest.

Police said four officers are deceased and seven injured.

Local TV stations showed protesters marching along a street in downtown, about half a mile from City Hall, when the shots erupted and the crowd scattered, seeking cover, the Associated Press reported. Civil rights activists have noted how police officers are rarely charged in fatal shootings and how, in many cases, key details often remain unknown, including the identities of many officers involved.

In the latest death, Reynolds and Castile were on the way home from getting him a haircut for his upcoming birthday, she told reporters, when they were stopped by police in the manicured St. Paul suburb of Falcon Heights for having a broken taillight. Her 4-year-old daughter was in the back seat. It was dusk.

In the video stream she posted live, Reynolds said her boyfriend had just told the officer he had a legal firearm and was retrieving his gun permit and driver’s license from his wallet when the officer opened fire. Blood had already spread across Castile’s white shirt, and he appeared to lose consciousness while the St. Anthony, Minn., police officer who shot him is seen in the background shouting: “I told him not to reach for it! I told him to get his hands up.”

In response, Reynolds said: “You told him to get his ID, sir, his driver’s license.” At one point, as Reynolds screamed in grief and frustration, her daughter could be heard trying to comfort her mother in a small voice, saying, “It’s okay, Mommy. It’s okay. I’m right here with you.”

“Please don’t tell me my boyfriend’s gone,” Reynolds pleads in the video. “He don’t deserve this, please. He works for St. Paul Public Schools. He’s never been in jail, anything. He’s not a gang member, anything.”

On Thursday, Reynolds said the officer fired five times, and she added that authorities did not check Castile for a pulse and that it took 15 minutes for paramedics to arrive.

“They killed him while he was still wearing his seat belt,” she said. “The officer was jittery from the second he pulled us over until he pulled the trigger.”

In his news conference, Dayton noted the lack of medical attention. “No one attended to his condition as they attended to the police officer involved. . . . The stark treatment, I find absolutely appalling at all levels.”

In an interview at their family’s home, Castile’s sister Allysza Castile showed a reporter a black 9mm handgun, with a loaded magazine, that she was keeping perched near their front door.

“I’m scared of the police,” she said. “They’re slaying us like animals.”

She said she had not slept since the shooting, and as she talked about her brother, she broke down in tears.

Allysza and Castile’s mother, Valerie, said they raced to the scene of the shooting Wednesday night when friends watching his girlfriend’s Facebook stream started calling. His mother said that no one from the family has seen his body. No one from the police department, the local, state or federal government has contacted them, she said.

“The man was executed in that car,” Valerie Castile said. “People need to be held accountable for what they do.”

She said she believes the police officer profiled her son because he was black and wore dreadlocks. She said she had taught her son, described by the principal at the school where he worked as devoted to children, to always comply with a police officer’s orders.  “I’ve seen how many times it happens where an African American man or an African American woman gets shot by the police,” she said.

She said Castile lived a clean life. “He was exercising his right to bear arms,” Valerie said, and owned a firearm to protect his home.

On Thursday night, Minnesota state officials named Jeronimo Yanez as the officer who shot and killed Castile during the traffic stop. The state agency investigating the shooting said that Yanez and Officer Joseph Kauser, who have both been with the St. Anthony Police Department for four years, were on administrative leave. The Minnesota Department of Public Safety, in a statement, said it has collected several videos of the shooting, though none from body-worn cameras on either officer.

The acting police chief of the St. Anthony Police Department, which provides service to the small, predominantly white and middle-class town of Falcon Heights, told reporters early Thursday that the department had not had an officer shooting in about 30 years.

Protesters on Thursday said they have zero faith that an investigation into the shooting would result in any charges. Their frustrations stem from both a state and federal probe into the death of Jamar Clark, a 24-year-old black man fatally shot by Minneapolis police during an encounter in November.

The Bureau of Criminal Apprehension — the same agency investigating Castile’s shooting — also investigated Clark’s death, and local prosecutors said in March that the officers would not face charges. The Justice Department came to a similar conclusion last month.

“I do not have faith in our justice system, whether it is the local level, the state level, the county level, the federal level,” said Nekima Levy-Pounds, president of the Minneapolis chapter of the NAACP. “How else do you hold officers accountable?”

A review by the StarTribune found that since 2000, at least 148 people have been killed by police officers in Minnesota. But the review found that, despite state investigations, no officers were charged in any of these deaths.

Castile’s mother noted that her son was killed just days before his birthday. He was born in St. Louis, and the family moved to the Twin Cities a few years later, living in the suburbs to get away from the inner city.

Known as Phil, he began working at age 13, she said, repairing bicycles for other children in the neighborhood and later helping to fix broken lawn mowers. He graduated from St. Paul’s Central High School and held jobs at a Blockbuster video store and Target before going to work for the St. Paul public school system’s nutrition services division in 2002.

Two years ago, he earned a promotion to a supervisory position at a new school: J.J. Hill Montessori Magnet School, where he managed the cafeteria.

“He loved kids, even though he didn’t have any of his own,” his mother said, noting that her son always helped out the children in need in the lunch line. “He’d give them an extra scoop of this and an extra scoop of that.”

She said that he was so dedicated to his job that when his car broke down, he paid $50 in cab fare to be able to make it in on time. Teachers and parents at J.J. Hill said they adored Castile, a warm and gentle presence who knew the names of each of the school’s more than 400 students.

“We’re just devastated,” said Anna Garnaas, who teaches first-, second- and third-graders at the school in St. Paul. “He knew the kids, and they loved him.”

Shapiro reported from St. Paul, Brown and Wan from Washington. Wesley Lowery, Michael E. Miller, Mark Berman, Lindsey Bever and Jennifer Jenkins in Washington and Todd Melby in St. Paul contributed to this report.

For a video, go to wapo.st/falconhts.