Criminal charges will soon be filed in the case of a six-year-old boy who spurred a frantic search for fear he was inside a wayward helium balloon, but who was later found safe at home, officials said.

The Larimer County Sheriff's department was preparing charges over the much-publicized incident. The boy's father, Richard Heene, an amateur scientist and inventor, has denied speculation Thursday's incident was a publicity stunt.

A massive search-and-rescue operation and media frenzy ensued after the Heene's homemade helium balloon broke loose and drifted thousands of feet above Colorado for hours.

"We do anticipate ... there will be some criminal charges filed in respect to this incident," said Sheriff Jim Alderden, speaking to reporters in a news conference televised on CNN.

He said initial charges would likely be a misdemeanor.

The department was preparing search warrants, he said, adding the possible misdemeanor charge "hardly seems serious enough given the circumstances." He said the department was in contact with federal authorities and additional federal charges were possible.

Heene and his wife Mayumi were both questioned by sheriff's officials yesterday.

Speculation over whether the four-hour ordeal was an elaborate hoax by the family -- who have appeared on reality television and are known as storm chasers -- arose after the boy, named Falcon, said on CNN's "Larry King Live" that he stayed hidden "for the show."

Earlier yesterday, father Heene reiterated it was not a publicity stunt. He had called media to his Fort Collins, Colorado home for what he said would be a major announcement, but instead requested that reporters put written questions into a box that he would address later.

"Was this some sort of publicity stunt?" asked a reporter outside the home.

"Absolutely no hoax," said Heene.

Falcon, whose older brother had reported seeing him climb into a compartment attached to the balloon, was discovered hiding in a box in the attic above his family's garage.

Alderden said the department would hold a news conference this morning.