The gap-toothed boy, famously pictured holding a baseball bat and wearing a red cap, went missing from the toy department of a mall in Hollywood, Florida, in July 1981. His head was found in a canal two weeks later, but his body was never found.

Hollywood police said that Otis Toole, a longtime suspect in the Walsh killing, was in fact the murderer. Toole died in prison in 1996.

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"For 27 years we've been asking, `Who could take a six-year-old boy and murder him and decapitate him? Who?"' John Walsh said at a news conference. "We needed to know. We needed to know. And today we know.

"The not knowing has been torture. But that journey's over."

Police said they decided to end the investigation and declare Toole as the killer after a thorough review of records.

The murder of Adam Walsh galvanized a movement to protect children from predators. John Walsh became a leading voice for missing and exploited children, and founded the Adam Walsh Child Resource Center.

He became the host of America's Most Wanted, a television show that debuted in 1988 to publicize and help capture fugitive crime suspects.

US President George W Bush signed the Adam Walsh Child Protection Act in 2006 to establish a national sex offender registry, and to make it harder for predators to reach children on the internet.

Toole was a partner of serial killer Henry Lee Lucas, and confessed to scores of murders. He admitted to killing Adam Walsh, but later recanted.

REUTERS