In a significant development, a federal appeals court has granted a new trial for Pedro Hernandez, who was previously convicted for the 1979 murder of 6-year-old Etan Patz. The case, which stands as one of the most infamous missing child cases in the United States, saw its guilty verdict overturned on Monday.

Since his arrest in 2012 and subsequent conviction in 2017, Hernandez has been serving a sentence of 25 years to life. The arrest came after an extensive and unsettling search that spanned decades, following Etan’s disappearance on the very day he was first permitted to walk by himself to his school bus stop in New York City.

The appeals court highlighted that the trial judge’s handling of a jury note during Hernandez’s 2017 trial was “clearly wrong” and “manifestly prejudicial.” This trial was his second, as his first trial in 2015 ended in a jury deadlock. Throughout, his lawyers have maintained his innocence.

The court ordered Hernandez’s release unless the 64-year-old gets a new trial within “a reasonable period.”

The Manhattan district attorney’s office, which prosecuted the case, said it was reviewing the decision. The trial predated current DA Alvin Bragg, a Democrat.

Harvey Fishbein, an attorney for Hernandez, declined to comment when reached Monday by phone.

A message seeking comment was sent to Etan’s parents. They spent decades pursuing an arrest, and then a conviction, in their son’s case and pressing to improve the handling of missing-child cases nationwide.

Etan was among the first missing children pictured on milk cartons. His case contributed to an era of fear among American families, making anxious parents more protective of kids who had been allowed to roam and play unsupervised in their neighborhoods.

The Patzes’ advocacy helped establish a national missing-children hotline and made it easier for law enforcement agencies to share information about such cases. The May 25 anniversary of Etan’s disappearance became National Missing Children’s Day.

“They waited and persevered for 35 years for justice for Etan which today, sadly, may have been lost,” former Manhattan DA Cyrus Vance Jr. said after hearing about Monday’s reversal. Vance, now in private practice, had prioritized reexamining the case and oversaw the trials.

Etan was a first grader who always wanted “to do everything that adults did,” his mother, Julie Patz, told jurors in 2017.

So on the morning of May 25, 1979, she agreed the boy could walk by himself to the school bus stop a block and a half away. She walked him downstairs, watched him walk part of the way and never saw him again.

For decades, Etan’s parents kept the same apartment and even phone number in case he might try to reach them.

Etan’s case spurred a huge search and an enduring, far-flung investigation. But no trace of him was ever found. A civil court declared him dead in 2001.

Hernandez was a teenager working at a convenience shop in Etan’s downtown Manhattan neighborhood when the boy vanished. Police met him while canvassing the area but didn’t suspect him until they got a 2012 tip that he’d made remarks years earlier about having killed a child in New York, not mentioning Etan’s name.

Hernandez then told police he’d lured Etan into the store’s basement by promising the boy a soda, then choked him because “something just took over me.” He said he put Etan, still alive, in a box and left it with curbside trash.

Hernandez’s lawyers said his confession was false, spurred by a mental illness that makes him confuse reality with imagination. He also has a very low IQ.

His daughter testified that he talked about seeing visions of angels and demons and once watered a dead tree branch, believing it would grow. Prosecutors suggested Hernandez faked or exaggerated his symptoms.

The defense pointed to another suspect, a convicted child molester who made incriminating statements years ago about Etan but denied killing him and later insisted he wasn’t involved in the boy’s disappearance. He was never charged.

The trials happened in a New York state court. Etan’s appeal eventually wound into federal court and revolved around Hernandez’ police interrogation in 2012.

Police questioned Hernandez for seven hours – and they said he confessed – before they read him his rights and started recording. Hernandez then repeated his admission on tape, at least twice.

During nine days of deliberations, jurors sent repeated queries about those statements. The last inquiry asked whether they had to disregard the two recorded confessions if they concluded that the first one was invalid.

The judge said no. The appeals court said the jury should have gotten a more thorough explanation of its options, which could have included disregarding all of the confessions.

Associated Press writers Larry Neumeister in New York and Eric Tucker in Washington contributed.