SAN FRANCISCO (CBS SF) — A San Francisco man was charged with murder Monday in the death of a 7-month-old boy who had been left in his care and died of traumatic head injuries, prosecutors announced Monday.

San Francisco District Attorney Chesa Boudin said that he has filed murder charges against Joseph Williams in the April 20th death of the little boy initially identified only as Baby S. Since then, the city’s Medical Examiner’s Office has identified the infant as Synciere Williams.

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Williams — who is not related to the little boy — was caring for the child when he brought the injured boy into the hospital. The child was declared dead a short time later.

“The death of Baby S is a tragedy,” Boudin said in a news release. “We are so deeply sorry for the family, whose enormous grief we can only imagine.”

“My office has filed murder charges and we will put every resource at our disposal into prosecuting this case,” he added. “We know nothing can make the family whole again, but we will work our hardest to make sure there is justice. Please know that our office is mourning with and for you.”

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Prosecutors said Williams has a known history of alleged domestic violence. In both cases, San Francisco police arrested Williams for suspected domestic violence against his girlfriend, but later released him without charges.

Prosecutor said the girlfriend is not the mother of Baby S.

In both prior cases, prosecutors carefully considered all of the facts collected by the police and concluded that, because the evidence could not prove that Williams, rather than the other party in the altercation, was criminally responsible for the incidents, the DA’s office could not ethically bring charges in the cases.

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“We believe the available facts of these two cases supported the decision to not move forward with charges, but that is not enough,” Boudin’s office said in a news release. “In light of this tragedy, we will be reviewing all policies related to charging domestic violence crimes, including discussions with our law enforcement partners to ensure we are all using best practices to obtain admissible evidence and to support victims.”