In the March primary election, Lacey had garnered significantly more voter support than Gascon but was unable at the time to claim the majority necessary to avoid a runoff.
The primary preceded the in-custody death of George Floyd in Minneapolis, which sparked nationwide protests and prompted calls for more aggressive prosecution of law enforcement officers involved in civilian deaths.
Lacey, the first woman and Black person to run the nation's largest local prosecutor's office, faced some of her harshest criticism from Black Lives Matter supporters due to her failure to prosecute police officers for fatal shootings.
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Meanwhile, Gascon, a former LAPD assistant chief of police and chief in two cities before becoming a prosecutor, has been harshly criticized by police unions and public safety groups for his support of aggressive criminal justice reform. He favors mental health and drug treatment over incarceration.
The campaign to run a DA's office with nearly 1,000 lawyers and a jurisdiction that covers the country's second largest city and 10 million residents in the nation's most populous county is seen by many as the crown jewel for progressives trying to reshape the way crime is prosecuted at the local level.
During the campaign, activists targeted Lacey, who replaced Steve Cooley as DA in 2012.