The 1979 disappearance of Etan Patz helped catalyze a national missing-children's movement. Six-year-old Etan was one of the first vanished children whose case was publicized in what became a high-profile way: on milk cartons. His disappearance also helped usher in an age of parental anxiety. On Friday, opening statements are set to be heard in the murder and kidnapping trial of Pedro Hernandez, who confessed in 2012. Here's a brief explanation of how Patz's disappearance and the ensuing murder case:

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A YOUNG BOY VANISHES

Etan Patz was walking to his Manhattan school bus stop alone for the first time when he disappeared May 25, 1979, igniting an exhaustive search and helping to make missing children a national cause in the United States. The anniversary of his disappearance, May 25, became National Missing Children's Day. His parents helped press for new laws that established a national hotline and made it easier for law enforcement agencies to share information about missing children. The movement grew after the kidnapping and killing of 6-year-old Adam Walsh in 1981 in Florida and other high-profile child abductions. Frightened parents soon stopped letting children walk alone to school and play unsupervised in their neighborhoods.

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AN INVESTIGATION SPANS CONTINENTS AND DECADES

Etan's body has never been found, but his family had him legally declared dead in 2001. The investigation stretched across decades and at one point reached Israel before police announced that Hernandez had confessed in May 2012. Then police got a tip shortly before the arrest of Pedro Hernandez, 54, of Maple Shade, New Jersey. He worked at a convenience store in Etan's neighborhood but had never been a suspect. Hernandez has pleaded not guilty. In his recorded confessions, Hernandez tranquilly recounts offering soda to entice Etan into the convenience store basement and choking him. He says he put the still-living boy into a plastic bag, boxed up the bag and left it on a street.

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A LONG-AWAITED DAY IN COURT

Prosecutors' case appears to center on Hernandez's confessions to them and police, plus statements authorities say he made to a friend, his ex-wife and a church prayer group in the 1980s about having harmed a child in New York. The prosecution team hasn't alluded to any physical evidence against Hernandez, and his defense has said there is none. Hernandez's defense maintains his confessions are the false imaginings of a man who has an IQ in the lowest 2 percent of the population and has problems discerning reality from fiction. Prosecutors call the confessions credible, and Manhattan state Supreme Court Justice Maxwell Wiley ruled they could be used at trial. The decision followed a weekslong 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.

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ANOTHER SUSPECT

The defense also wants jurors to consider longtime 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'd invoke his rights against self-incrimination, but some evidence about the investigation into Ramos will be allowed.