The county sheriff's department had presented two charges against Mami Matsuura-Berhow, the mother of 16-year-old Nathaniel Tennosuke Berhow.
The teen opened fire with a gun assembled at home -- shooting five schoolmates, including two who were fatally wounded, before before taking his own life on Nov. 14 -- his birthday.
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The Santa Clarita Valley Signal says detectives wanted to charge Berhow's mother for contributing to the delinquency of a minor and criminal storage of a firearm.
However, the case was rejected last month due to lack of evidence.
The anniversary of the shooting is Saturday.
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