Pamela Price, a new district attorney in Northern California, is the latest to reopen cases that had seemingly been shut, including one from more than 15 years ago.Agustin Gonsalez was shot dead in 2018 by police officers in Hayward, Calif., when he refused to drop a sharp object during a confrontation on a dark street.Andrew Moppin-Buckskin was killed by Oakland officers in 2007 after he ran away following a car chase, hid under a vehicle and failed to comply with their demands.Two years ago, Mario Gonzalez died after he was pinned on the ground for more than five minutes by officers in Alameda, Calif.In all three cases, prosecutors determined that the police should not be criminally charged, seemingly closing the book.But shortly after she became the district attorney of Alameda County in January, Pamela Price initiated a new review of those cases and five others in one of the most extensive re-examinations of police killings launched by progressive prosecutors.Ms. Price’s review is notable because her predecessors had already cleared the officers of wrongdoing and two of the reopened cases occurred more than 15 years ago.As high-profile instances of police brutality shocked the public in recent years and raised questions about official law enforcement accounts, liberal prosecutors campaigned on the promise that they would review cases that they felt were hastily closed without charges. Their efforts to revisit old cases have won praise from the activists and liberal Democrats who voted for them.But the re-examinations so far have rarely led to criminal charges.“To reopen a police use-of-force case is, in many ways, a herculean task,” said Steve Descano, the commonwealth’s attorney in Fairfax County, Va. He lost in court after he charged two federal Park Police officers for the 2017 shooting of a man who fled a car crash, a case that the Justice Department previously reviewed and declined to pursue.The incidents almost never have evidence as stark as the bystander video showing George Floyd being pinned to the ground in 2020 for more than nine minutes by Derek Chauvin, a former Minneapolis police officer who was convicted of murdering Mr. Floyd.The circumstances often are more ambiguous, the footage less telling. And once a district attorney writes a lengthy memo detailing why criminal charges are unjustified against a police officer, it can be difficult for a successor to overcome those arguments, absent new evidence.“Everybody is going to go through it again, and the outcome in all probability is going to be the same,” said Jim Pasco, the executive director of the National Fraternal Order of Police. “And what’s Einstein’s definition of insanity?”The biggest hurdle for pursuing criminal charges is the wide latitude that officers have to use force. State legislatures, including California’s, have tried to narrow that ability. But officers generally can still use lethal force when they feel they or others could be killed, a level of immunity that law enforcement officials say is necessary to ensure the public’s safety.Pamela Price, the new district attorney of Alameda County, Calif., announced this year that she would review eight police killings, including one dating to 2007.Jim Wilson/The New York TimesAlameda County, Ms. Price’s jurisdiction, covers a large swath of the East Bay across from San Francisco, containing 14 cities and numerous police departments. In the county seat of Oakland, where the Black Panther Party emerged in the 1960s, a legacy of radical politics is intertwined with a troubled history of law enforcement. The Oakland Police Department has been under federal oversight for more than two decades.Ms. Price campaigned on a liberal platform that, besides reviewing old cases, included removing local residents from death row and resentencing inmates serving life sentences — an effort, she said, to restore public trust. Since taking office, she has directed her staff to seek the lowest possible prison sentence for most crimes.She said that in the past, prosecutors routinely gave officers a pass when they killed someone on the job, and she wants questionable police killings to face the same rigor that other criminal cases get.“Every case that we’re looking at now was determined under a double standard,” Ms. Price said in an interview. “Police officers received a different standard of justice than everyday people.”Ms. Price is among a growing cadre of progressive prosecutors elected over the last decade, beginning with the 2016 elections of Kim Foxx in Chicago and Kimberly Gardner in St. Louis, on promises of reducing jail populations and holding police accountable. The movement gained steam after Floyd’s murder.Some prominent district attorneys have since faced a backlash over crime concerns. Chesa Boudin was recalled last year in San Francisco, while Ms. Gardner resigned last week as she faced criticism for her handling of violent crime. Ms. Foxx is not running for re-election next year and has endured criticism from moderates and conservatives, especially for her support of eliminating cash bail statewide.In Maine, a police officer has never been prosecuted for an on-duty killing. But in July 2020, Natasha Irving, the district attorney for four counties, said she would seek charges for the 2007 police shooting death of Gregori Jackson, who was drunk and ran away after a routine traffic stop in Waldoboro, the town where Ms. Irving grew up.Three years later, however, Ms. Irving said that based on the attorney general’s review of the forensics from the case, she will not file charges.“It’s just not going to be a provable case,” she said in an interview.Karla Gonsalez stood at a memorial to her son at the site in Hayward, Calif., where he was shot and killed by police officers.Jim Wilson/The New York TimesIn the Virginia case pursued by Mr. Descano, Bijan Ghaisar, 25, was involved in a minor car crash and then fled in his Jeep, pursued by two officers who cornered Mr. Ghaisar in a residential neighborhood. When the vehicle moved toward a police car, they opened fire, killing him.Mr. Descano brought a case, but a judge dismissed the charges, ruling the officers reasonably feared they were in danger. His efforts to pursue the case further were rejected by the state’s attorney general and the Justice Department.Such reviews offer the possibility of justice for still grieving families but also may unrealistically raise their hopes. Karla Gonsalez, the mother of Mr. Gonsalez, the man who was killed in Hayward, said she was torn when she heard Ms. Price was reopening her son’s case.Television outlets began replaying the body camera footage of Mr. Gonsalez’s confrontation with police. For his family, all of the anger, grief and unresolved questions came rushing back. Why had the officers not tried to de-escalate the situation?“I was excited to know that it was going to be opened up again,” Ms. Gonsalez said. “At the same time, I was very nervous that it was going to be another roadblock, another failure.”Less than 2 percent of police killings result in charges, according to Philip M. Stinson, a professor of criminal justice at Bowling Green State University. That figure has not budged since 2020. The number of people killed by the police is holding steady — last year it was 1,200, compared with 1,147 in 2022, according to Mapping Police Violence.“From where I sit, nothing has changed,” Mr. Stinson said.In Los Angeles County, George Gascón, who was elected district attorney in 2020, appointed a special prosecutor to reopen four cases in which his predecessor declined to file charges.Ryan Young for The New York TimesIn Los Angeles County, George Gascón, who was elected district attorney in 2020, appointed a special prosecutor to reopen four cases in which his predecessor, Jackie Lacey, declined to file charges. He also asked an independent team of experts to review more than 300 previous use-of-force cases to see if the evidence warranted criminal charges.The special prosecutor, Lawrence Middleton, had secured convictions in a 1993 federal trial against Los Angeles Police Department officers for beating Rodney King. In the new cases, he has secured indictments against two officers in the 2018 shooting death of Christopher Deandre Mitchell, who was driving a stolen vehicle and had an air rifle between his legs when he was confronted by officers in a grocery store parking lot. (“Both officers’ use of deadly force was reasonable under the circumstances,” Ms. Lacey wrote in a 2019 memo.)The re-examinations themselves take time, and liberal prosecutors may yet file criminal charges against more officers in past cases. But they said that charges should not be the only benchmark of whether their reviews are worthwhile.“I think there is huge value to reopening a case if there is probable cause, or if there is evidence that seems compelling in any way,” Ms. Irving, the prosecutor in Maine, said. “Yes, part of it is to send a message to people who would be bad actors. Part of it is to send a message to families that have lost loved ones, or individuals who have been harmed, that they count.”Ed Obayashi, a California-based expert in use of force who trains law enforcement, said in 2021 that Mario Gonzalez did not seem to be a threat to the public in Alameda and questioned why officers restrained him before he died. The police had responded to a call that Mr. Gonzalez, 26, was acting strangely in a park and talking to himself.Mr. Obayashi said this week that he did not fault Ms. Price for reviewing the case, but he also felt that if there was consensus in the Alameda County District Attorney’s Office under her predecessor, Ms. Price should not have reopened it.“It’s a big concern to law enforcement because these types of decisions, to revisit old cases that former prosecutors have decided that no charges should be brought against the officer, it’s political,” Mr. Obayashi said. “It’s politically driven.”Ms. Price’s review also includes two cases from 15 years ago that occurred seven months apart and involved the same officer killing men who ran away after traffic stops, including Mr. Moppin-Buckskin. The officer, Hector Jimenez, was cleared in each case and remains with the Oakland Police Department.“For the life of me I can’t understand what Ms. Price thinks she’s doing with those kinds of cases, some 15 years after they occurred,” said Michael Rains, a lawyer for Mr. Jimenez.In Hayward, the city agreed to pay $3.3 million to settle a federal lawsuit with Agustin Gonsalez’s family but said it was a way to support his children rather than an admission of wrongdoing. The city said in April that there appeared to be no new evidence that warranted reopening the case.Mr. Gonsalez was shot in November 2018 after police officers confronted him. He was suicidal and was holding a razor blade. He refused to drop the blade and approached the officers with his arms outstretched. That’s when the two veteran police officers shot him 12 times.Karla Gonsalez recently sat in her sister’s kitchen and described her son as a father of two who was an Oakland sports fan and often drove nearly 400 miles south to Disneyland with his season pass. In the corner of her living room was a makeshift shrine, with a flickering candle and a crucifix draped over his portrait.Cynthia Nunes, Mr. Gonsalez’s cousin, said her family was grateful his case was being reopened. But they want more.“Charges actually have to be brought forward, too,” she said. “The system needs to change.”Julie Bosman More