O'Malley says the evidence is not there, but Grant's family members are vowing to keep the fight going.
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"My heart hurts today because for 12 years I've been crying out for justice for my son," says Oscar Grant's mom Wanda Johnson, as she fought back tears Monday.
"My son's head was smashed against the wall and he was kicked and he was punched and the officer, Pirone, still walks around free today," says Johnson.
A 2019 independent report found Pirone struck Grant in the head and kneed him. Pirone can be seen holding Grant down in video.
A newly released report by O'Malley's office found that there was no injury to Grant's head or neck that contributed to his death, adding that former officer Johannes Mehserle fired the fatal shot and was previously convicted of involuntary manslaughter.
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"We conclude that we cannot prove Pirone guilty beyond a reasonable doubt nor was there enough evidence to charge him with murder in 2009 and there is not enough evidence now," O'Malley said.
Grant's family tells us that more than 50,000 people have signed a petition demanding that Pirone be charged. That petition can be found here.
"Tony Pirone committed murder on that platform and he should be charged with felony murder," says Oscar Grant's Uncle Cephus Johnson, known to many in the community as "Uncle Bobby."
Grant's family members say their fight isn't over and that those from BART and the city will address this issue Tuesday morning.
A detailed video statement and a 16 page legal report and analysis from the DA's office can be accessed here.