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The Anaheim, Calif., police officer who shot and killed a young Latino man last summer – one of a number of police shootings that sparked protests and national media attention – was cleared of charges and deemed legally justified in his actions, the district attorney said after an investigation..

The finding in the July 21, 2012, shooting death of Manuel Diaz was announced in a letter Wednesday by Orange County District Attorney Tony Rackauckas.

The shooting by Officer Nicholas Bennallack and the next day's killing of another man by a different Anaheim police officer sparked a series of demonstrations, some of which turned violent.

The finding angered Diaz's mother, Genevieve Huizar, who pledged to protest in front of the local courthouse.

"The D.A. appointed himself the judge and jury for this officer. I'm never going to stop fighting until Nick Bennallack is in prison," Huizar told The Orange County Register.

In the wake of the announcement, the ACLU Foundation on Thursday sent the Anaheim City Council a letter asking it to create a civilian review board for police shootings.

Ruth Ruiz, the city's spokeswoman, did not immediately return a call seeking comment about the letter.

Police said Diaz and his two companions ran when they were approached by officers. Police also said Diaz was a documented gang member from Santa Ana, an allegation his family has denied.

The letter of findings includes statements from the officers and witnesses, a rundown of the evidence, details from the autopsy, and a summary of YouTube video taken after the shooting. It also includes details on Diaz's criminal history and Bennallack's job history, along with a legal analysis of the shooting.

"It is our legal opinion that the evidence does not support a finding of criminal culpability on the part of Officer Bennallack, and that there is significant evidence that the officer's actions were reasonable and justified under the circumstances when he shot Diaz," the letter states.

Bennallack cannot be charged with a crime because the prosecution would be unable to prove beyond a reasonable doubt that he didn't act in self-defense or the defense of others when he shot Diaz, the district attorney wrote.

"Diaz may have been holding a gun," the letter reads.

Three facts are provided to support that possibility: Diaz had a prior felony conviction for possessing a gun for the "benefit of the gang," a cellphone found nearby included photos of Diaz posing with a gun days earlier, and a raid weeks later on gang members found 40 guns.

The findings also say Bennallack had good reason to believe Diaz posed a danger because witness statements indicated Diaz brought an object out of his waistband and raised it as he turned toward officers.

Though the object does not match the description of a handgun, the letter said there must be an "allowance for the 'split-second judgments in tense circumstances' required of Officer Bennallack."

Because Bennallack believed Diaz was pulling a gun from his waistband, the letter stated, it was "not disproportional" to respond with deadly force, even if Bennallack could have responded with his stun gun instead.

Diaz's family has filed a $50 million wrongful death lawsuit against the officer and the city.

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