A man has gone on trial in New York accused of murdering a child whose disappearance in 1979 helped spark a national missing children's movement.

Pedro Hernandez, 53, is charged with kidnapping and killing Etan Patz, who was one of the first missing US youngsters to feature on the side of a milk carton.

Etan's parents helped push for legislation that created a nationwide framework for such cases.

The new laws established a hotline and made it easier for agencies to share information about youngsters who disappeared.

And the anniversary of his disappearance in 1983 became National Missing Children's Day.

Six-year-old Etan was walking from his house to his Manhattan school bus stop alone for the first time on 25 May, 1979, when he disappeared.

It led to a widespread search but his body has never been found and his family had him legally declared dead in 2001.

At the time Etan went missing, Hernandez was a teenager working in a shop in the child's neighbourhood.

He was not a suspect until 2012 and was arrested following a tip-off.

Police announced he had confessed in May of that year - but he has since recanted his confession and pleaded not guilty to the charges.

In his reported recorded confessions, Hernandez recounted offering a soft drink to entice the boy into the convenience store basement and choking him.

He said he put the boy, who was still alive, into a plastic bag, boxed up the bag and left it on a street.

Hernandez's defence team maintains his confessions are the false imaginings of a man who has an IQ in the lowest 2% of the population and has problems distinguishing reality from fiction.

Prosecutors call the confessions credible and NY Supreme Court Justice Maxwell Wiley ruled they could be used at trial.

The decision followed a weeks-long hearing on whether Hernandez was properly advised of his rights to stay silent and mentally capable of understanding them.

Hernandez has taken anti-psychotic medication for years and has been diagnosed with schizotypal personality disorder, which includes the characteristics of social isolation and odd beliefs.

The defence also wants jurors to consider long-time suspect Jose Ramos, a convicted Pennsylvania child molester.

A civil court declared Ramos responsible for Etan's death after he rebuffed questioning, but he was never criminally charged and has denied involvement.

Ramos has refused to testify at Hernandez's trial, saying he would invoke his rights against self-incrimination, but some evidence about the investigation into Ramos will be allowed.