This story was co-published with NPR

In August 2011, federal agents swept across the Detroit area, arresting doctors, pharmacists and other health professionals accused of running a massive scheme to defraud Medicare.

The following month, several of those arrested —including psychiatrist Mark Greenbain and podiatrist Anmy Tran — were suspended from billing the state's Medicaid program for the poor.

"Health care fraud steals funds from programs designed to benefit patients, and we all pay for it," U.S. Attorney Barbara McQuade said in a press release at the time of the arrests. "We hope that the strength of our efforts will have a deterrent effect."

But the indictment and Medicaid suspensions didn't deter Medicare from continuing to allow the doctors to treat elderly and disabled patients — and billing taxpayers for their services.

In 2012, Medicare paid Greenbain more than $862,000, according to newly released data on Medicare payments to physicians. Tran received $155,000.

Greenbain and Tran were among dozens of doctors identified by ProPublica who Medicare kept paying after they were suspended or terminated from state Medicaid programs, indicted or charged with fraud, or had settled civil allegations of submitting false claims to Medicare.

Outlays to these doctors amounted to more than $6 million in 2012, ProPublica's analysis shows. That's a small fraction of the $77 billion Medicare has publicly reported paying that year for doctors' visits and outpatient services in its Part B program, but it signifies a hole in regulators' ability to protect the program — and patients — against fraud and abuse, said current and former government officials and fraud experts.

The total dollars paid to sanctioned doctors is likely much higher. Only a handful of states post online the names of doctors terminated from Medicaid programs in a way that can be accurately matched to Medicare Part B payments.

"If you've been suspended or terminated in one of the federal programs...I would think that you'd be suspended in the other programs, just as a basis of good practice," said Louis Saccoccio, chief executive of the National Health Care Anti-Fraud Association.

Part B payments to doctors were released last week for the first time. A court injunction that had kept the information secret for 35 years was lifted last year as a result of a lawsuit by Dow Jones & Co., parent company of the Wall Street Journal.

But Medicare has long had access to the information. "They're the ones doing the paying," Saccoccio said.

Aaron Albright, a spokesman for the Centers for Medicare and Medicaid Services, said he could not discuss the status of individuals, such as Greenbain and Tran, both of whom were finally barred from billing Medicare this month.

By that time, Greenbain had pleaded guilty and been sentenced to four years in prison. Tran had been found guilty and trial and was sentenced to five years. She is appealing her conviction.

Albright said the Medicare payment data may not reflect money already recovered by his agency or held back from providers suspended from billing the program.

Preventing improper payments is a top priority for CMS, Albright said. The agency has employed new enrollment screening techniques to prevent high-risk providers from getting into the system and is using advanced data analytics to spot fraudulent billing before payments are made, he said. "Already, we have cracked down on tens of thousands health care providers suspected of Medicare fraud," he said in an email.

Medicare's fraud-fighting efforts have been criticized repeatedly in recent years. In an audit released last month, the inspector general of the U.S. Department of Health and Human Services found that about one-third of states hadn't told CMS when they terminated providers from Medicaid and others had provided incomplete information, hobbling regulators' ability to flag sanctioned professionals.

In December, the inspector general faulted Medicare for not systematically reviewing the billings of the program's top-paid doctors and said it should be doing more to spot aberrant claims.

Last year, ProPublica reported that doctors who had been terminated from Medicaid or had been disciplined by state medical boards were able to continue prescribing medications to beneficiaries in Medicare's drug program, prompting Sen. Charles Grassley (R-Iowa) to push for better coordination.

Medicare has more direct responsibility for overseeing activities in Part B than in the drug program, which is administered by private insurers. The drug program doesn't even require that prescribers be enrolled in Medicare and payments go to pharmacies, not doctors. By contrast, in Part B, it's up to Medicare to monitor services and payments, which go to clinicians or their employers.

"There's been a disconnect between Medicaid and Medicare on problem providers," wrote Grassley, ranking Republican on the Senate Judiciary Committee, in an email to ProPublica. "The release of Medicare billing data should help force better communication between Medicaid and Medicare on these providers. The new transparency makes it harder to ignore when doctors who harm patients or defraud taxpayers in one program face no consequences in the other program."

Sen. Tom Carper, (D-Del.), chair of the Senate Homeland Security and Governmental Affairs Committee, credited Medicare with ramping up efforts to verify the credentials of those treating its beneficiaries. "But there is still much work to be done," he said in a statement.

Among the physicians ProPublica found who continued to collect Medicare payments after being flagged by law enforcement or other oversight agencies:

Dr. Lawrence Eppelbaum, a Roswell, Ga., pain doctor convicted last year of inducing patients to be treated at his Atlanta pain clinic by paying their travel fees through a purported charity he controlled. He was indicted on the charges in March 2011, but Medicare paid him $500,000 to treat 80 patients the following year. This February, Eppelbaum was sentenced to 50 months in prison and fined $3.5 million. He is appealing.

In a sentencing memorandum, Eppelbaum's lawyer maintained that Medicare did not lose any money because of the doctor's conduct. "Virtually every patient would have received treatment somewhere, by some doctor," he wrote. "Thus, Medicare would have paid the exact same amount of money, albeit possibly to another provider."

Michigan ophthalmologist Matthew Burman was suspended by the state's Medicaid program in 2009 after he was convicted of a misdemeanor count of criminal sexual conduct arising from a patient's accusation against him. He subsequently surrendered his medical licenses in Texas and California and agreed not to activate his registration in New York. He was paid $379,000 by Medicare in 2012. (Medicare has not released payment data for prior years.)

Burman, who continues to practice in Michigan, said he could have re-enrolled in Medicaid but chose not to. "One has nothing to do with the other," he said. "I didn't violate any Medicare rules. Medicare has nothing to do with why I'm not a Medicaid provider."

Las Vegas pain doctor Steven Kozmary agreed in December 2011 to pay the federal government $1 million to settle health care fraud allegations involving Medicare and other programs. The government could have moved to terminate him from Medicare, according to the settlement. Instead, in 2012, Medicare paid him $563,000. He was disciplined by Nevada's medical board in 2013 related to the 2011 settlement. He did not return a phone call.

Louisville Dr. Steven Stern and his practice paid $350,000 to settle allegations of overbilling Medicare in September 2011. He and his practice were accused of overbilling Medicare for infusing Infliximab, a drug used to treat rheumatoid arthritis. Specifically, they were accused of splitting vials of the drug across multiple patients but billing as if a whole vial was used for each. In 2012, Stern received more than $3 million in payments from Medicare, including $2 million for infusing Infliximab. He did not return a phone call seeking comment.

Eight of 14 New Jersey health providers arrested in December 2011 on charges of receiving kickbacks for referring Medicare and Medicaid patients to a specific MRI center continued to be paid by Medicare in 2012. At the time of the arrests, Tom O'Donnell, special agent in charge for the HHS inspector general said, "The audacity of these physicians should offend honest taxpayers, especially at a time when our taxpayer resources are stretched thin."

Even a guilty plea sometimes wasn't enough for Medicare to cut off payments. Dr. Anthony Jase of New Orleans pleaded guilty to two counts of health care fraud in October 2011. He still collected $97,460 for Medicare billings in 2012. Last fall, he was sentenced to 15 months in prison and ordered to pay $360,293 in restitution.

"It certainly looks like there is a need for more attention," said Mark McClellan, former administrator at CMS who is now at the Brookings Institution. "One important consequence of the release of this information at the physician level is that it will lead to some further analysis and actions against these truly outlier physicians who are clearly billing improperly."

ProPublica's analysis also found payments to doctors who were subsequently barred from billing the program by the HHS inspector general, mostly because of fraud convictions. Medicare paid 135 of them more than $18 million in 2012, before they were kicked out.

Some doctors have been indicted post-2012, including Michigan oncologist Farid Fata, a Michigan oncologist who was paid $10 million in 2012, ranking him among Medicare's top-paid providers that year. Last year, Fata was accused of misdiagnosing patients with cancer so he could give them unnecessary, expensive treatments. Fata has pleaded not guilty; his lawyer did not respond to a request for comment.

In a conference call last week with reporters, CMS' principal deputy administrator Jonathan Blum said the agency knows it can do more to find fraud. "We know that there's waste in the system. We know that there's fraud in the system. We want the public's help" to review the physician payment data and report suspected wrongdoing.