California has adopted one of the nation’s strictest laws regulating police use of force, hoping it will deter shootings by law enforcement agents.

Gov. Gavin Newsom on Monday signed Assembly Bill 392, which changes the standard for police officers’ justified use of deadly force from instances when it’s “reasonable’’ to when it’s “necessary.’’

The law redefines when police can resort to deadly force “based on the totality of the circumstances’’ and encourages the use of de-escalation techniques and crisis-intervention methods.

“We are doing something today that stretches the boundary of possibility and sends a message to people all across this country that they can do more and they can do better to meet this moment,” Newsom said as he stood alongside family members of people killed by police.

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Modifications to the previous law, advocated by activist groups like Black Lives Matter, were prompted by officer-involved shootings such as the March 2018 killing of Stephon Clark, an unarmed black man gunned down outside his grandparents’ house in the state capital of Sacramento when police mistook his cellphone for a firearm.

Newsom said the new law will reduce the number of lives lost and begin to heal communities.

The measure by Democratic Assemblywoman Shirley Weber of San Diego, which initially met fierce resistance from law enforcement organizations, made it through the state Legislature with bipartisan support after it was amended to address police concerns.

The law still contains the strongest language of any state, according to the American Civil Liberties Union, which proposed the bill and negotiated the changes.

Weber said the law “changes the culture of policing in California.” It is linked to a pending Senate bill requiring that officers be trained in de-escalating confrontations and finding alternatives to using lethal force.

Newsom’s signature on the new California law comes on the same day the New York Police Department announced the firing of Daniel Pantaleo, the officer who put petty-crime suspect Eric Garner in a chokehold that contributed to his death in July 2014. Garner’s repeated cries of “I can’t breathe’’ as he gasped for air became a rallying cry in the movement against police brutality.

Similarly, Clark’s death at 22 precipitated major protests and demands for changes and a higher level of police accountability. The officers who shot him were ruled to have acted lawfully and were not disciplined.

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Joy Johnson, a pastor who leads a faith-based advocacy organization in Sacramento, was among those who commemorated the anniversary of Clark’s death in March while pushing for a legal change.

“We’re trying to raise the public’s consciousness to see that, if you say you followed the law to the letter and the law says it’s justifiable to take the life of an unarmed person, then we believe the law needs reexamining,’’ she said.

On Monday, the law’s reexamination resulted in a significant change.

Contributing: The Associated Press