The Supreme Court on Monday reinstated a murder conviction in the 1979 case of Etan Patz, a 6-year-old boy who was living in New York City. 

In a 6-3 ruling, the justices granted an appeal from New York prosecutors who asked the high court to overturn a federal appeals court ruling that overturned the verdict. Prosecutors were preparing to try Pedro Herdandez for a third time in the case. His first trial ended in a mistrial, the Associated Press reported. 

The U.S. Court of Appeals for the Second Circuit reversed Hernandez's conviction on murder and kidnapping charges in the second trial, over how the judge had answered a question from jurors. 

Manhattan District Attorney Alvin Bragg said the reasoning was "a slender reed" that ignored all the evidence presented over the course of a five-month trial, which included 66 witnesses. 

In an unsigned opinion, the justices agreed that federal courts should not overturn state courts, citing a 1996 federal law that was intended to reduce federal court oversight of state criminal trials. 

Hernandez, 64, is serving a sentence of 25 years to life in prison. His lawyers said they are "terribly disappointed" in the high court's ruling, and they insisted their client is serving time for a crime he didn't commit.