The Supreme Court reinstated the murder conviction of the man who abducted and murdered Etan Patz in 1979. 

Pedro Hernandez, 64, had his conviction for murdering the six-year-old reversed last year by a federal appeals court. 

In an unsigned opinion, the Supreme Court reinstated the conviction with a 6-3 vote; all three liberal justices dissented.

Hernandez was convicted in 2017 of killing Patz in 1979, after confessing he'd lured the youngster to a basement in Manhattan's SoHo neighborhood. 

Prosecutors were preparing to try him for a third time and urged the Supreme Court to undo the decision to overturn the verdict that was given last year. 

The unanimous panel of the U.S. Court of Appeals for the Second Circuit reversed Hernandez' murder and kidnapping conviction in the second trial because of how the judge had answered a question from jurors.

Manhattan District Attorney Alvin Bragg had called the basis for overturning the conviction 'a slender reed' that essentially ignored a five-month-long trial with 66 witnesses.

The justices agreed, in an unsigned opinion, that federal courts should not second-guess state courts under a 1996 federal law that was intended to reduce federal court oversight of state criminal trials.

'The Second Circuit exceeded its authority in holding that Hernandez is entitled to relief,' the court wrote, referring to the New York-based appeals court.

Etan vanished while walking to his downtown Manhattan school bus stop on May 25, 1979. 

Hernandez worked at a nearby convenience shop at the time, but the Maple Shade, New Jersey, resident didn't become a suspect until 2012.

Etan was among the first missing children ever to appear on milk cartons, and the anniversary of his disappearance became National Missing Children's Day.

Hernandez admitted to the crime under police questioning, but his lawyers say he confessed falsely because of a mental illness that sometimes made him hallucinate. 

They emphasized that the admission came after police queried him for about seven hours before reading him his rights and recording the interview. 

Hernandez then repeated his confession on tape, at least twice. He was arrested in 2012 and first went on trial for Patz' murder in 2015, but the prosecution ended in a hung jury before a second trial saw him convicted following over nine days of deliberations. 

Etan's body was never recovered. Hernandez - who was 18 at the time of Etan's disappearance - said that he dumped the boy's remains in the garbage. No physical evidence was ever produced to verify this. 

Hernandez's lawyers argued at the time of his arrest in 2012 that he suffered from schizotypal personality disorder, which can cause hallucinations, and that he had a low IQ 'at the border of intellectual disability.' 

The crux of the decision to overturn Hernandez's conviction hinged on a confession he made to police in 2012. 

He had never before been a suspect, but his family reported to cops that he had confessed during a prayer group to killing a child in New York at the time of Etan's disappearance. 

Under interrogation, Hernandez - who worked in a bodega near to where the boy's bus stop was - again confessed to luring Etan into a basement by promising him soda. 

'Something just took over me,' he said in a recorded confession. 'I felt so sorry.' 

Hernandez's attorneys attempted to have the interrogation confession thrown out, arguing that the 'confession in one of the nation's most notorious child disappearances was false, peppered with questionable claims and made after almost seven hours of police questioning.' 

He had confessed before his Miranda Rights were read to him, and detectives then had him repeat the confession on video after they were read. 

Etan's disappearance stunned New York City and led to nationwide searches when he vanished over four decades ago, and it is remembered by many Americans as a watershed moment in the end of parents allowing their children to move around unattended. 

His case is often credited for ushering in an age of heightened attention on the cases of missing children. 

He became the first child pictured on milk carton campaigns, where the cases of missing children were put on the labels of milk cartons in hopes of bringing attention to their investigations.

The anniversary of Etan's disappearance also became National Missing Children's Day.