By Pat Reber

Washington, Oct 18 (DPA) Colorado justice officials have said they expect to file criminal charges in the case of the experimental runaway helium balloon thought mistakenly to have been carrying aloft a six-year-old boy.

Sheriff Jim Alderden of Larimer County, Colorado, who earlier dismissed the suggestion that the dramatic flight and fears were a hoax, indicated Saturday he would consult with federal officials to find out if more serious charges could be brought.

The class-three misdemeanour charges available at the local level of justice "hardly seem serious enough given the circumstances", Alderden said in broadcast remarks.

"So what we're going to have to do is back up a little to talk to the district attorney, (Federal Aviation Administration) officials and federal officials to see if there aren't any federal charges that would be more appropriate than what we are able to do locally," he said.

The father of the boy, Richard Heene, has denied repeatedly that the incident Thursday was a publicity stunt for the experimental helium balloon he had designed and built and kept in his backyard.

Law enforcement officials, military and media aircraft chased the helium-filled balloon for two hours as live broadcasts held the country transfixed. But when it landed, the child, Falcon, was no longer on board.

After rising fears Falcon had fallen out, he was found hiding in a box in the attic apparently scared of getting a scolding from his dad. He had never been on board.

Alderden called in Heene and his wife Miyumi for a second round of interviews Saturday afternoon before announcing he had made "some significant progress in this investigation".

The sheriff also planned to seek search warrants for Heene's home that would likely be used to examine computer and phone records.

Heene and has family have participated in TV reality shows such as "Wife Swap" and there were questions about whether he had created a stunt to capture media attention and boost his profile.

The drama began midday Thursday when one of Falcon's two brothers reported that the flying saucer-shaped balloon had inadvertently taken off after the child had climbed into it. After authorities were alerted, news helicopters began tracking the helium-filled craft as pictures of the drama played out and rescuers tried to figure out how to get the balloon under control.

After a two-hour journey the balloon crash-landed in a Colorado field, but the boy was not found inside prompting fears that he may have fallen out. Though a police search of the family's house and surrounding areas failed to locate the boy, he eventually came out by himself from his hiding place in a box above the garage.

The five-member Heene family has been giving daily television interviews to the major broadcast and cable networks, during which the child Falcon has thrown up several times from the excitement.

Speculation that the incident may have been staged increased when Falcon looked at his father during a CNN remote interview and said, "You said, 'We did this for the show'." Heene, a scientific tinkerer and storm chaser, looked at his child sternly, then dismissed such speculation as "pathetic".

In another round of interviews Saturday, the CNN reporter tried to pin Falcon down about what he meant with the "show" remark.

This time, Heene refused to relay the question.

"I am kind of appalled that after all the feelings I experienced up and down that you are asking this," Heene said, ending the interview.