The couple's lawyer, David Lane, said earlier in the day that he expected charges to be filed by Wednesday. With television cameras and reporters set up outside the Heene home, Lane has stressed that the Heenes are willing to turn themselves in to avoid the spectacle of a public arrest.
Lane declined to say directly whether he believes the incident was a hoax but said the Heenes are innocent unless convicted. The family remained in seclusion Monday at their home.
"If they (prosecutors) can prove their case beyond a reasonable doubt, that's one thing. If they can't prove their case beyond a reasonable doubt, that's another," he told The Associated Press.
Investigators also say they want to question an associate of his after e-mails surfaced showing the two had discussed a balloon hoax months ago as part of a public relations campaign for the reality show.
Robert Thomas of Denver claimed Heene had told him he was planning a media stunt to promote a proposed reality show. Thomas, a self-described researcher, sold his story to Gawker.com and provided the Web site with e-mail exchanges between him and Heene. Thomas said the show would feature Heene as a mad scientist who carries out various scientific experiments.
"This will be the most significant UFO-related news event to take place since the Roswell Crash of 1947, and the result will be a dramatic increase in local and national awareness about The Heene Family, our Reality Series, as well as the UFO Phenomenon in general," according to a copy of the show's proposal provided to the site by Thomas.
Gawker.com editor-in-chief Gabriel Snyder confirmed the New York-based Web site paid Thomas, but declined to say how much for the story billed with the headline: "Exclusive: I Helped Richard Heene Plan a Balloon Hoax."
Snyder said Thomas was planning to meet with investigators but Larimer County sheriff's spokeswoman Kathy Messick wouldn't comment on whether he had been interviewed. Messages left for Thomas by The Associated Press were not returned.
Thomas, 25, said in his Gawker.com story that the plan he knew about did not involve Heene's children.
The emergence of the e-mails is the latest twist in a story that played out live on national television on Thursday when a silver helium-filled balloon floated away from the Heenes' home with 6-year-old Falcon believed to be aboard. But he was never in the balloon.
Some flights at Denver International Airport had to be changed to a different runway, but the airport remained open during the balloon's flight, airport spokesman Chuck Cannon said Monday. Previous reports said the airport was temporarily shut down.
The National Guard provided two helicopters in an attempt to rescue the child, costing several thousand dollars. When the balloon landed without the boy, officials thought he had fallen out and began the grim search for his body.
Sheriff Jim Alderden announced Sunday that he's seeking charges, including felonies, against Richard and Mayumi Heene. Alderden said the stunt two weeks in the planning was a marketing ploy by the Heenes, who met in acting school in Hollywood and have twice appeared on ABC's reality show "Wife Swap."
"We certainly know that there's a conspiracy between the husband and wife, you've probably seen some of the e-mails and some of the things on the Internet suggesting that there may be other conspirators," Alderden said.
Alderden said documents show that a media outlet has agreed to pay money to the Heenes with regard to the balloon incident. Alderden didn't name the media outlet but said it was a show that blurs "the line between entertainment and news."
It wasn't clear whether the deal was signed before or after the alleged hoax, or whether the media outlet was a possible conspirator.
"Let's call it (my statement) short of speculation that a media outlet was in on the hoax, but let's not discount the possibility," he said.
In an e-mail Sunday to the AP, Snyder said editors at Gawker.com had not contacted the Heene family or offered them money for their story, referring to Alderden's reference to a deal being struck by a media outlet.
"No, that wasn't us," Snyder said.
The sheriff said he expected to recommend charges of conspiracy, contributing to the delinquency of a minor, making a false report to authorities and attempting to influence a public servant. Federal charges were also possible.
The most serious charges are felonies and carry a maximum sentence of six years in prison and a $500,000 fine. Alderden said they would be seeking restitution for the costs, though he didn't have an estimate.
As Alderden told reporters Sunday that the whole thing was a hoax, the Heenes were shopping for snacks at Wal-Mart, where Richard Heene told the AP he was "seeking counsel."
"This thing has become so convoluted," Heene said, tears welling in his eyes. He said his wife was holding together better than he was.
Once investigators got a good look at the "flying saucer" they determined that the thin mylar balloon covered with foil and held together with duct tape would not have been able to launch with the 37-pound-boy inside, according to Colorado State University physics professor Brian Jones.
Alderden said he didn't know whether the 6-year-old had been hiding in the rafters of the family's garage during an intense five-hour search, as the family claimed.
"For all we know he may have been two blocks down the road playing on the swing in the city park," the sheriff said. The sheriff said all three of the Heenes' sons knew of the hoax, but likely won't face charges because of their ages. The oldest son is 10.
Alderden said investigators had an "aha" moment that the story was a hoax when Falcon turned to his father during a CNN interview Thursday and said what sounded like "you had said we did this for a show" when asked why he didn't come out of his hiding place.
On Friday, Falcon got sick during two separate TV interviews when asked again why he hid.
Alderden said they didn't question the family Friday because they wanted to keep the family's cooperation by maintaining the appearance that they believed their story. That's the same day the sheriff gave a press conference in which he said he believed the saga was a "real event." He said Sunday that those assurances were part of his effort to keep the family's trust.
Records show that police have responded to the house at least twice in the past year, including a possible domestic violence incident in February. No charges were filed.
Alderden said officials tried Saturday to persuade Mayumi Heene, 45, to go to a safe house, but she declined.
Alderden said the children were still with the parents Sunday and that child protective services had been contacted to investigate their well-being. On "Wife Swap," Heene was portrayed as erratic, at one point throwing a glass of milk on a participant on the program.
"Clearly, from all indications, Mr. Heene has somewhat of a temper," Alderden said.
Lane said Alderden should "put up or shut up" about domestic violence.
"For the sheriff to put out for public consumption that Richard is a wife beater and not have any charges even considered to be filed is irresponsible and is designed solely to turn the public even more against the Heenes, in particular Richard," Lane said.
Heene has a profile listed on a Web site that helps people get cast in reality shows, and the producer of "Wife Swap" said it had a show in development with the Heenes but the deal is now off. TLC also said Heene had pitched a reality show to the network months ago, but it passed on the offer.
Associated Press writers Catherine Tsai, Dan Elliott and AP contributor Breck Larson in Fort Collins provided material for this report.