DENVER (Reuters) - The flight of a home-made helium balloon that touched off a frantic rescue attempt for the young boy thought to be aboard was a publicity-seeking hoax, a Colorado sheriff said on Sunday.

Larimer County Sheriff Jim Alderden said the parents of 6-year-old Falcon Heene would likely face four charges in the bizarre incident, which riveted television viewers across the United States for more than two hours on Thursday.

The airship took to the skies on Thursday morning and Richard and Mayumi Heene claimed that their son had climbed aboard, triggering a massive search and rescue operation as the odd silver craft drifted for 50 miles, trailed by U.S. National Guard helicopters.

The boy was later found not in the flying saucer-shaped craft but safe at home.

“It has been determined that this is a hoax, that it was a publicity stunt,” Alderden told a press conference.

“We believe we have evidence at this point to indicate that it was a publicity stunt done with the hopes of better marketing themselves for a reality television show at some point in the future,” he said.

Alderden said the parents could be charged with conspiracy, contributing to the delinquency of a minor, making a false police report and attempting to influence a public servant.

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Investigators think Falcon and his brothers, who are 8 and 10, were “100 percent involved” in the caper, he said, but were not expected to face criminal charges because of their age.

“On the bizarre meter, this rates a 10,” Alderden said.

A lawyer hired by Richard and Mayumi Heene, David Lane, told local KUSA-TV that the incident had been a “nightmare” for the family.

Lane said the parents would be willing to turn themselves in to law enforcement to avoid “the public spectacle and humiliation” of being arrested in front of their children.

‘THEY PUT ON A GOOD SHOW’

Authorities had considered desperate measures to somehow bring the balloon down safely before it slowly began to deflate on its own and landed softly in a wheat field near Denver.

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Rescuers who raced to the balloon and found it empty then began to scour the countryside for Falcon, fearing that he had fallen out -- until the family announced that he was safe and had been hiding in a garage attic.

Questions were raised after a CNN interviewer told Richard Heene to ask his son why he had stayed in hiding so long when searchers were desperately calling his name.

The boy responded: “You guys (his parents) said that, um, we did this for the show.”

The Heene family has appeared on the ABC television reality show “Wife Swap” in which families swap mothers to deal with family issues.

They gave interviews on a series of U.S. morning shows on Friday to emphatically deny the incident was staged. Falcon vomited repeatedly on camera.

Alderden, who told reporters on Friday that he was inclined to believe the Heenes, said his investigators determined that the incident was staged after interviewing all five members of the family and searching their home.

“This has been a planned event for some two weeks,” he said. “The plan was to launch the spacecraft for a reality TV show. The plan was to create a situation where it appeared that Falcon was in the craft to gain publicity. To obtain notoriety,

to obtain publicity for a television show.”

The sheriff said he initially let reporters, and the Heenes, think that he bought their story as a way to gain the family’s trust but privately harbored skepticism.

Richard Heene has been described as a storm chaser and amateur scientist who had involved his wife and sons in his activities. He told reporters that his contraption was intended as an experimental vehicle that “people can pull out of their garage and hover above traffic 50 to 100 feet.”

But Alderden portrayed the Heenes essentially as hucksters desperate to get on television.

“They are actors. Not only have they appeared on TV, they met at acting school in Hollywood,” Alderden said. “They put on a very good show for us, and we bought it.”