Tristan Beaudette was murdered in June. A transient known to frequent the area was charged with his killing.
The claim names the Los Angeles County Sheriff's Department and several state and local agencies.
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Beaudette's family alleges the public was not warned about a series of unsolved shootings in the park prior to his death, and that the park negligently failed to provide a safe space for him and his children.
Sheriff's and park officials were not immediately commenting.