The attorneys allege the lead detective in the case, Farmington Police Cpl. Russ Bradford, bought a house from Willis in 2007. Santa Fe attorney Mark Donatelli and John Day said the transaction compromises the investigation.
"Our motions raise some serious questions on what's going on here," Day said.
Their motion does not name Bradford, but he is described as the detective who swore to the criminal complaints against Willis. Those complaints are signed by Bradford.
Bradford declined to comment Monday on the allegations. "I'm not going to respond to that until I have a chance to read it," he said.
Willis' lawyers said Bradford purchased a home from their client in December 2007 for about $100,000 less than the listed price.
"Although it is unclear why the detective received such a financial boon, what is clear is that he had substantial financial transactions with Mr. Willis," the attorneys said in the motion filed in Farmington Magistrate Court.
"Because these cases involve allegations regarding Mr. Willis' financial dealings, the detective likely is a witness. And even if he is not, his objectivity regarding Mr. Willis is suspect," they added.
Dustin O'Brien, chief deputy district attorney, said the allegations against Bradford are unfounded and do not compromise the investigation.
"They've just alleged that he bought a house," O'Brien said. "We don't believe that there's any conflict or problem. Just having some kind of relationship or business is insufficient. There has to be some bias or motivation for there to be misconduct. To our knowledge, there wasn't anything unusual about any business transaction that (Bradford) was in."
Bradford has been the lead investigator in the case for months, following Willis' trail from Kirtland to Branson, Mo. Willis' attorneys now say Bradford's involvement in the case constitutes misconduct.
"It is highly inappropriate for a lead investigator to target someone with whom he has had a significant financial transaction," they said in Monday's filing. "The fact that he purchased a home from Mr. Willis at a significant discount the circumstances of which are unknown, seriously undermines his credibility and calls into question his motives."
The unexpected twist is the latest development in the case against Willis, who is at the center of a sprawling white-collar crime investigation involving millions of dollars.
Willis is wanted on two active arrest warrants on suspicion of embezzlement, racketeering, fraud and securities fraud. Authorities are looking for him.
Last week, Donatelli said in a court filing that Willis is undergoing medical treatment for a variety of conditions, and he intends to appear in court. Donatelli said Willis has remained in close contact and "fully intends to appear in court as required, provided that his medical condition permits him to do so."
Donatelli claims Willis was hospitalized due to hypertension, chest discomfort, visual difficulties and several minor strokes. He said Willis is taking nearly 20 medications for the maladies. He did not reveal Willis' location.
Monday's motion to dismiss the charges came as the investigation against Willis appears to be intensifying. Last week, authorities seized $362,000 in cash from properties in Branson owned by Willis.
Law enforcement searched three houses and an office building in Branson that Willis owns, Bradford said. In addition to the U.S. currency, the Internal Revenue Service seized an unspecified amount of foreign currency and gems.
Donatelli asked Magistrate Judge Mark Hawkinson to quash the arrest warrants in a Sept. 24 filing, saying incarceration would jeopardize Willis' health.
Hawkinson on Sept. 26 apparently denied the motion, then rescinded that action. Hawkinson then set a hearing in the case for Oct. 11.
Willis is wanted on suspicion of embezzling gems and jewelry worth millions from a former business associate. He's also under investigation in connection with the collapse of New Mexico Title Co. and New Mexico Title Escrow Co., which closed in late January amid complaints of missing funds.
The arrest warrants focus on Willis' business dealings with Mike Atchison and Quentin Smith, two former associates.