POST FALLS - The on-scene investigation into Thursday's fire that destroyed a riverfront Post Falls mansion owned by a couple with financial woes ended on Tuesday with no clues on how the blaze started.

Members of the State Fire Marshal's Office and the federal Alcohol, Tobacco, Firearms and Explosives joined Kootenai County Fire and Rescue in the search on Tuesday and were done investigating the rubble by early afternoon.

"We have not found a thing," said Dan Ryan, KCFR division chief. "At least for the on-scene investigation, nothing has turned up to let us know what the cause may have been."

The 11,000-square-foot home at 1504 E. Plaza, which was assessed at $1.5 million, has been owned by Len and Pam Wallace for the past 10 years. It was slated to be foreclosed upon last Friday, the day after the fire.

Ryan said the extent of the fire damage made it difficult to find clues on how the fire started.

Petroleum-sniffing dogs were on scene on Friday and, while some samples were sent to a lab, Ryan said there were no obvious hits that pointed toward arson.

"We're hoping to get preliminary lab results in a few days," said Ryan, adding that a lot of products are made with petroleum and it can be difficult to pinpoint if something was used as an accelerant.

Police, meanwhile, continue their part of the investigation, including gathering witness statements.

"Unless some new information develops, we're pretty much at a dead end," Ryan said.

Len Wallace speculated that the fire may have been associated with one of seven fireplaces at the home.

No one was home during the fire as the water had been shut off due to water damage caused by the dishwasher, Len said.

Police have interviewed the Wallaces, along with their two male teens who lived in the home, and said all of their testimonies as to the circumstances before the fire were consistent with each other.

The Wallaces have gone to bankruptcy court multiple times to protect their assets.

Len Wallace said he was close to staving off foreclosure. He said the family had been moving belongings from the home in the days leading up to the fire - as reported by neighbors - due to "an unstable situation."

The home, built in 1986, is next door to the so-called Amway House on the Spokane River that was used to award businesses that sold household products well.

The Wallaces formerly owned the guest house on the property of the burned home before it was lost to foreclosure. Both it and the Amway house were spared from the fire.

Wallace said he was a victim of what he believes was a business fraud in Montana. He said he invested in a company that has products that identify dairy cows and, after he tried to get out and get his money back, there was a judgement against him.

The decision in 2003 awarded MagTrac Bolus, LLC, a $2.5 million judgement against Wallace for damages. Wallace then had five unsuccessful appeals to the Montana Supreme Court.

Wallace had plans to develop about 900 acres of property south of Post Falls on Blossom Mountain known as Raspberry Ridge until the economy went in the tank.

Wallace operated the controversial Big Velvet Ranch in the 1990s south of Darby, Mont. It was an enclosed 2,000-acre elk farm used for "shoot for pay" hunting.