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The helium balloon constructed by the Heene family travelled more than 80 kilometres after it broke free of its tethers on Thursday. ((KMGH-TV/Associated Press))

Authorities in Colorado have no proof that Falcon Heene's family was carrying out a hoax when they reported he was in a helium balloon that floated away from their home, the Larimer County sheriff says.

However, police plan to interview the Heene family again Saturday, in light of questions raised about the incident after six-year-old Falcon said "We did this for a show" in an interview with CNN on Thursday night, Sheriff Jim Alderden said at a news conference Friday.

Falcon was found safely at home Thursday, hiding in the attic of his family's garage in Fort Collins, more than two hours after the escaped balloon travelled more than 80 kilometres while being followed on live television.

While investigating whether the incident was a hoax, police consulted an expert at Colorado State University who confirmed the balloon had the capacity to carry a payload of 80 pounds (36.3 kilograms), Alderden said. That means it was capable of carrying Falcon, who weighs about 37 pounds, he added.

The boys' parents — Richard Heene and his wife, Mayumi — first called the Federal Aviation Authority for help, then a news channel with a helicopter and finally 911, Alderden said, adding their logic made sense, given the sheriff's office's lack of experience in this kind of event.

The Heenes are storm chasers who appeared in the ABC reality show Wife Swap. They said they were conducting an experiment with the flying saucer-like craft that involved allowing it to rise about six metres off the ground in their backyard where it was tethered, but it became untied and floated away.

Initially, Falcon told police he thought he was responsible for the balloon coming untied and hid because he was afraid he'd be in trouble,  Alderden said.

If police uncover evidence that the incident was a hoax, the Heenes could be charged with making a false report, which is classified as a third-class misdemeanor, a minor offence, Alderden said.

Richard Heene said he was upset at the suggestion of a hoax because his family isn't trying to promote anything and has nothing to gain from the ordeal.

"I'm kind of appalled after all the feelings that I went through, up and down, that you guys are trying to suggest something else," he said. "This is what we do all the time," he said of the homemade balloon, which he had wanted to use as a low-altitude vehicle.

Heene told KUSA-TV in Denver that in making the "show" comment, his young son had a long day and was confused by the extra people around the house and the number of questions he was being asked by reporters.

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Six-year-old Falcon Heene sits in the box of his family's pickup truck outside their home after he was found hiding in the garage. ((David Zalubowski/Associated Press))

Falcon appeared tired and vomited twice when his family was asked about his comment regarding the "show" during separate television interviews on several U.S. networks on Friday morning.

Military aircraft, including a Black Hawk helicopter that costs more than $4,600 US an hour to operate, participated in the rescue efforts for about three hours. Departures at Denver International Airport were briefly halted and air traffic controllers rerouted planes in the area.

Alderden declined to speculate on how much the rescue effort cost, saying "that is the least of our worries."

Neighbour Bob Licko, 65, said the family was in a commotion outside the house Thursday when the balloon got away from the backyard. The two other children were on the roof with a camera and the mother looked distraught.

Licko said he didn't think the incident was a hoax. "They're better actors than I thought they were if that's the case," he said.

With files from The Associated Press