Since 1999, Medicare has spent $8.2 billion to procure power wheelchairs and scooters for 2.7 million people. Today, the federal government does not know how much of that money was actually paid to scammers.

In his testimony, Fernandez noted that the clinic was in a second-floor walk-up.

“I had to climb the stairs,” Fernandez said, in order for the doctor to proclaim him unfit to climb stairs.

After seeing the doctor, prosecutors said, both Cortez and Fernandez got power wheelchairs from Fadojutimi’s company. The company then sent Medicare the bills. Medicare paid.

Today, Cortez’s wheelchair sits in his garage, still wrapped in plastic from the factory. Fernandez’s wheelchair is occupied by an enormous stuffed animal wearing a Los Angeles Lakers hat.

“I put my little teddy bear on top of it,” Fernandez said, as jurors smiled at a photo of the bear in the chair.

An overwhelmed system

Fraud in Medicare has been a top concern in Washington for decades, in part because the program’s mistakes are so expensive. In fiscal 2013, for instance, Medicare paid out almost $50 billion in “improper payments.” These were bills that, upon further reflection, contained mistakes and should not have been paid.

No one knows how much of that money was actually lost to fraud, and how much of it was caused by innocent errors.

The power-wheelchair scam provided a painful and expensive example of why Medicare fraud works so often. The fault lay partly with Congress, which designed this system to be fast and generous. And it lay partly with Medicare bureaucrats — who were slow to recognize the threat and use the powers they had to stop it. As a result, scammers took advantage of a system that was overwhelmed by its own claims and lacked the manpower and money to check most of those claims before it paid.

The scheme first appeared in the mid-1990s in Miami — a city whose mix of elderly people and professional scammers has always made it the DARPA of Medicare fraud, where bad ideas begin.

“The patients would be walking,” said one former Justice Department official, recalling investigations from that time. “And they’d have the wheelchair, a $2,500 wheelchair, sitting in the corner with stacks of [stuff] on it. And [investigators] would say, ‘Why do you have this?’ And they would say, ‘They told me I could have this, so I took it.’ ”

Fraudsters, they were learning, had invented a new twist on an old trick: the Medicare equipment scam.

The original equipment scam had sprung up in the 1970s, at a time when Medicare was young and criminals were still learning how to steal its money. Doctors, for example, could bill Medicare for exams they didn’t do. Hospitals could bill for tests that patients didn’t need.

The equipment scam was the poor man’s way in, an entry-level fraud that didn’t require a medical degree or a hospital.

Instead, the crooks only had to set up a “medical equipment” company and get access to the Medicare system. Then, they needed to learn a simple scheme, in which the fraudster would run the normal order of medical decision-making in reverse.

A legitimate medical-supply company, of course, must wait for a patient to see a doctor, then come looking for somebody to fill a prescription. But a fraudster starts with a prescription he wants to fill.

Then he goes looking for a patient and a doctor to foist it on.

By the 1990s, fraudsters had already perfected parts of this equipment scam. To find the patients, for instance, they had learned to use professional recruiters, called “marketers” or “cappers.”

These recruiters induced seniors to hand over their Medicare ID numbers. Sometimes, they just paid the patients a bribe. Other times, they talked them into giving the number up free. The government is offering free wheelchairs, but only for a limited time. If you don’t act now . . .

Most fraudsters had also learned to buy off a doctor or two, paying a set price for each bogus prescription. But some had also perfected a cheaper method.

They corrupted dead doctors instead.

“The Russian mob up in Brooklyn has been doing this for years. . . . They scour the obits. They find out when Doctor Morris has died. They immediately write to Medicare and they say, ‘Hi, I’m Doctor Morris, and I’m changing my address,' ” said Lewis Morris, a former top official at the Department of Health and Human Services’ office of the inspector general.

If it works, the dead doctor’s mail is delivered to the live crook. Including paperwork with the doctor’s Medicare ID number. “So the new Doctor Morris, Sammy Scumbag, starts writing scrip in the name of Doctor Morris,” Morris said. Recent reforms have lessened this problem.

The payoff of this whole scheme came when a scammer sent Medicare a bill. The bill would say that the bought-off doctor had prescribed some piece of equipment to the bought-off (or hoodwinked) patient.

The fraudster would say that he had supplied that thing. Now, he wanted Medicare to pay its share — usually, 80 percent of the price tag.

But what was the best kind of equipment to use?