WASHINGTON (AP) — Republican presidential contender Ben Carson has maintained a business relationship with a close friend convicted of defrauding insurance companies and testified on his behalf, even as the candidate has called for such crimes to be punished harshly.

Pittsburgh dentist Alfonso A. Costa pleaded guilty to a felony count of health care fraud after an FBI probe into his oral surgery practice found he had charged for procedures he never performed, according to court records.

Though the crime carries a potential sentence of up to 10 years in federal prison, Costa was able to avoid prison time after Carson helped petition a federal judge for leniency.

That's different from the position Carson took in 2013 as he prepared to launch his presidential campaign, saying those convicted of health care fraud should go to prison for at least a decade and be forced to forfeit "all of one's personal possessions."

At Costa's 2008 sentencing hearing, Carson described the dentist as "one my closest, if not my very closest friend."

"We became friends about a decade ago because we discovered that we were so much alike and shared the same values and principles that govern our lives," Carson told the judge, adding that their families vacationed together and that they were involved in "joint projects."

"Next to my wife of 32 years, there is no one on this planet that I trust more than Al Costa," Carson said.

Costa has served on the board of Carson's charity, the Carson Scholars Fund, and continues to lead the charity's fundraising efforts in the Pittsburgh area to provide $1,000 college scholarships to children in need.

Before his criminal conviction and the revocation of his license to practice dentistry, Costa built a multimillion-dollar fortune through commercial real estate. Investments Carson and his wife made through Costa earn the couple between $200,000 and $2 million a year, according to financial records that Carson was required to file when he declared his candidacy.

Costa also continues to promote his involvement with Carson's charity as part of his real estate business, prominently featuring the logo of the Carson Scholars Fund on the company's website. His son has worked with Carson's presidential campaign and a political committee founded by the retired neurosurgeon.

Doug Watts, the campaign's spokesman, said Wednesday he was unable to immediately respond to specific questions about land deals involving Carson and Costa. The AP contacted Watts on Tuesday and again Wednesday.

"I will confirm they are best friends and that they do hold business investments together," Watts said.

Costa did not respond to messages seeking comment.

The breadth of the two men's business ties has not been previously reported, partly because details can be obscured in property and incorporation records. Costa's company and its affiliates own properties in at least five states and overseas.

In 2007, a few months before Costa was charged, records show that a pair of corporations was established in Pennsylvania called BenCan LLC, and INBS LLC. Carson and his wife are listed as the sole members of the companies. Though the Carsons live outside Baltimore, the mailing address on the incorporation forms was Costa's home address in Pittsburgh.

BenCan and INBS then paid more than $3 million to purchase an office building in suburban Pittsburgh. The mailing address for the corporations listed on the deed matches the office of Costa's real estate firm, Costa Land Co.

That September, federal prosecutors charged Costa, accusing him of fraud committed over a nearly five-year period, according to court records. Investigators determined that Costa's dental practice charged more than 50 patients for procedures that had not been performed, resulting in a loss of more than $40,000 to insurance companies.

After Costa pleaded guilty, 40 of his family members, friends and dental patients wrote letters to the judge as character witnesses. Carson was one of three people who also testified at Costa's 2008 sentencing hearing, stressing his friend's charitable works and vouching for his personal integrity. Also testifying on Costa's behalf was Jerome Bettis, a beloved former Pittsburgh Stealers running back who had helped bring home a Super Bowl trophy to the city two years earlier.

The government urged the judge to make an example of Costa.

"Reduction of a sentence based on good works by a wealthy person can create the appearance that a defendant's financial resources and prominent connections can skew the justice system in ways not available to persons of lesser means," a prosecutor told the judge.

In the end, Costa got no prison time. He was sentenced to one year of house arrest and 100 hours of community service, and ordered to pay more than $294,000 in fines and restitution. Costa later got 12 months shaved off his three-year probation.

Though Costa was assigned to serve his sentence in his 8,300-square-foot mansion in nearby Fox Chapel, his lawyers repeatedly returned to court to seek permission for him to travel. A few months after starting his sentence, Costa asked to travel to the White House as one of 10 invited guests at a June 2008 ceremony where President George W. Bush presented Carson with the Presidential Medal of Freedom.

The judge denied that request, though Costa was later allowed to take a month-long trip to the Italian coast while on probation to handle what his lawyer described as urgent business at a resort he owns.

Carson's appeal for leniency toward Costa contradicts the draconian criminal penalties he called for in his 2013 political treatise, "America the Beautiful." In his book, Carson wrote that anyone found guilty of health care fraud should face what he called the "Saudi Arabian Solution."

"Why don't people steal very often in Saudi Arabia?" Carson asked. "Obviously because the punishment is the amputation of one or more fingers. I would not advocate chopping off people's limbs, but there would be some very stiff penalties for this kind of fraud, such as loss of one's medical license for life, no less than 10 years in prison, and loss of all of one's personal possessions."

Despite the tough-on-crime message, Carson and his wife kept their investment with Costa in the years since his conviction. Tax bills for the Pittsburgh office building owned by the couple are mailed to Costa Land Co. A recent lease for a portion of the property was signed on the Carsons' behalf by the president of Costa's company.

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Associated Press researcher Monika Mathur in Washington contributed to this report.

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