The AG's Office took over this case in May of 2021 after Solano County District Attorney Krishna Abrams recused herself.
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Monterrosa's family had a private meeting with AG Bonta and others on Tuesday.
They were brought there not knowing the outcome of this investigation and told on the spot.
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In June of 2020, Vallejo Police Officer Jarrett Tonn shot and killed Monterrosa from the back seat of an unmarked police vehicle through the windshield.
Monterrosa was outside a Walgreens where there had been a looting in the wake of George Floyd's killing.
At the time, police said Monterrosa had been running towards a car but suddenly stopped taking a kneeling position and that as he raised his hands he revealed something in his sweatshirt pocket.
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It turned out to be a hammer. According to the AG's Office, there was insufficient evidence to prove beyond a reasonable doubt that the officer did not act in self-defense or in defense of his partner officers.
"It is extremely disappointing that they decided not to move forward with criminal charges. We believe that there is more than sufficient evidence not only in our civil case that runs along parallel lines but enough evidence to bring criminal charges against Jarrett Tonn. We're looking forward to a review at the federal level," said Lee Merritt, attorney for the Monterrosa family.
VIDEO: Vallejo police release bodycam footage from fatal shooting of Sean Monterrosa
Vallejo PD release bodycam video from fatal shooting
The AG's Office also found that there was insufficient evidence to bring charges for the destruction of evidence in this case, the vehicle's damaged windshield which was discarded.
By text Tuesday afternoon, Michelle Monterrosa told ABC7 News I-Team reporter Melanie Woodrow she was disappointed, but won't stop fighting.
Take a look at more stories by the ABC7 News I-Team.