Spyros Panos M.D., was an orthopedic surgeon practicing in New York. For years, he seemed like a successful orthopedic surgeon, seeing dozens of patients a day and bringing in millions of dollars in fees for his suburban New York medical group.

Behind the scenes, however, he was inflating charges and billing for surgeries he didn’t perform, perpetrating a years-long fraud that culminated in a guilty plea on a single count in federal court in 2013. In 2013, he surrendered his license to practice medicine following his conviction for health care fraud.

In 2014, Panos began serving a 54-month sentence, and was released in 2016 to a halfway house and then, about a month later, to home confinement. He also faced more than 250 malpractice lawsuits, including some claiming that he botched surgeries.

Since March 2017, he has been serving a two-year term of supervised release. It did not take him long to get into trouble again. But even as he was waiting to be sentenced, federal prosecutors say, Panos was beginning a new criminal scheme that would go undetected for years until he was arrested again in April 2018.

In April 2018, he was charged with wire fraud, health care fraud, and aggravated identity theft, in connection with a scheme in which he assumed the identity of a licensed orthopedic surgeon and obtained over $860,000 in payments for reviewing patient files in Workers Compensation cases.

In about December 2013, after Panos pled guilty on October 31, 2013, and before he surrendered to serve his sentence on April 2, 2014, a company called Excel O LLC was formed. The registered agent for Excel O is a Panos family member and is not a licensed physician. Panos allegedly used this company to hide his identity, and assume the stolen identity of another physician, to dupe utilization review companies who evaluated cases nationwide.

In the latest criminal case, prosecutors say Panos defrauded six utilization review companies for $876,000, using a fake Google email address, a shell company registered in the name of a family member to a Brooklyn address and the credentials of another physician. He is charged with infiltrating an obscure but essential piece of the American health-care business: a $4 billion industry that provides independent doctors to render expert opinions on which treatments are appropriate. He has plead not guilty to the charges.

Over the past five months, thousands of patients have received notices from several insurance companies that Panos had posed as another doctor in order to review their medical records in coverage disputes. At least 2,500 people nationwide were affected, according to data compiled by Bloomberg, but the full reach of the alleged fraud hasn’t been made public.

Prosecutors did not name the six independent review companies that Panos worked for, but disclosure letters identify some of them: Advanced Medical Reviews and Network Medical Review are both subsidiaries of a company called ExamWorks, which was acquired by the private equity firm Leonard Green & Partners LP for $2 billion in 2016.

At least one company, Gallagher Bassett, a subsidiary of insurance brokerage Arthur J. Gallagher, told California authorities last August, that 1,294 workers’ compensation claims in the state may have been affected through vendors who hired Panos.