Maurice Hastings served more than 38 years in prison for the 1983 murder of Roberta Wydermyer in California.
New DNA evidence has instead pointed to another man who died in prison in 2020.
LA County District Attorney George Gascón described the now 69-year-old's 1988 conviction as a "terrible injustice".
"The justice system is not perfect, and when we learn of new evidence which causes us to lose confidence in a conviction, it is our obligation to act swiftly," he added in a statement.
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