NEW YORK • A jury has convicted a man of kidnapping and murdering a six-year-old boy in New York almost 40 years ago, in a case that still haunts US parents and changed how child abductions are handled.

Etan Patz vanished on May 25, 1979, after leaving his parents' home in Manhattan to walk alone for the first time to the school bus stop.

His parents discovered the boy was missing after he failed to return home from school at the end of the day.

His body was never found and the case was one of the city's great unsolved crimes for decades.

His disappearance also awakened Americans to the dangers of child abduction and fuelled a generation of hyper-vigilant child-rearing by parents terrified of letting their children out of their sight.

Pedro Hernandez, who was 18 at the time and worked at a convenience store near the bus stop, was convicted on Tuesday at the end of a second trial - after a jury failed to reach a unanimous verdict in 2015.

On Tuesday, the jury returned a verdict of murder in the second degree and kidnapping in the first degree after nine days of deliberations at the State Supreme Court in Manhattan.

Etan's father Stan Patz, a photographer whose pictures of his son were the first of a missing child featured on milk cartons in a nationwide search, thanked the prosecutors and the jury for returning the verdict.

"The Patz family has waited a long time but we finally have found some measure of justice for our wonderful little boy Etan," he told reporters.

"I am really grateful that this jury finally came back with what I have known for a long time, that this man Pedro Hernandez is guilty of doing something really terrible so many years ago," he said.

Hernandez, 56, confessed to police in 2012 that he killed Etan in the basement of the convenience store before dumping his body out with the trash.

But he later retracted his confession and pleaded not guilty.

Defence lawyer Harvey Fishbein vowed to appeal.

He argued that Hernandez had an IQ of 70, which would put him in the bottom 2 per cent of the population.

He added that a convicted sex offender named Jose Ramos was the real culprit.

Hernandez is to be sentenced on Feb 28, said a clerk to Judge Maxwell Wiley, who presided over both trials.

AGENCE FRANCE-PRESSE