Linda O'Keefe disappeared while walking home from school in a blue and white dress on Friday, July 6, 1973. The next morning, authorities discovered her strangled body in Back Bay.
Homicide investigators reviewed the evidence several times, but never found her killer.
In July 2018, the Newport Beach Police Department launched a social media effort to tell O'Keefe's story in her own voice on the anniversary of her disappearance.
The Orange County District Attorney's Office and Newport police will hold a joint press conference Wednesday morning with more details on the arrest.