David Williams, a personal trainer, spent years posing as a doctor and billing the nation’s top insurers, making off with millions of dollars.

Williams called himself “Dr. Dave” because he had a Ph.D. in kinesiology. But he didn’t have a medical license. Yet he wrongfully obtained, with breathtaking ease, federal identification numbers that allowed him to fraudulently bill insurers as a physician for services to about 1,000 people.

Getting one through the federal government’s Medicare program is a rite of passage for medical professionals and organizations. Without it, they can’t bill insurers for their services.

Williams discovered and exploited an astonishing loophole: Medicare doesn’t check NPI applications for accuracy. Instead, as one federal prosecutor later noted in court, Medicare “relies on the honesty of applicants.”

Williams first applied for an NPI under his own name as far back as 2008. But it wasn’t until 2014 that Williams began to ramp up his scheme, even though now he wasn’t just unlicensed, he was a two-time felon.

He got a second NPI under the company name, Kinesiology Specialists. The following year, he picked up another under Mansfield Therapy Associates. In 2016, he obtained at least 11 more, often for entities he created in the areas where he found fitness clients: Dallas, Nevada, North Texas and more. By 2017, he had 20 NPIs, each allowing him a new stream of billings.

For every NPI application, Williams also obtained a new employer identification number, which is used for tax purposes. But he never hid who he was, using his real name, address, phone number and email address on the applications. He added the title “Dr.” and listed his credentials as “PhD.” Under medical specialty he often indicated he was a “sports medicine” doctor and provided a license number, even though he wasn’t a physician and didn’t have a medical license.

“Now accepting most health insurance plans,” his Get Fit With Dave website announced. He added a drop-down menu to his site, allowing potential clients to select their health insurance provider: Aetna. Blue Cross Blue Shield. United.

He began building a team, soliciting trainers from the strength and conditioning department at Texas Christian University. He met with new recruits at local fast food joints or coffee shops to set them up. To the trainers, the business appeared legit: They even signed tax forms. Before long, Williams’ network stretched throughout Texas and into Colorado, Idaho and Nevada.

He used his favorite billing code – 99215. The code is supposed to be used less often because it requires a comprehensive examination and sophisticated medical decision-making, warranting higher reimbursement. In all, Williams used the code to bill United for more than $20.5 million – without apparently triggering any red flags at the insurer. For that code alone, the insurance giant rewarded him with $2.5 million in payments.

He ran the scheme for more than four years, fraudulently billing several of the nation’s top insurance companies – United, Aetna and Cigna – for $25 million and reaping about $4 million in cash.

A case summary, prepared by the Texas Department of Insurance, shows it first learned of the Williams case in January 2015 but lacked staff to investigate.

Cigna appears to have been the quickest to intervene. In January 2015, Cigna sent Williams a letter, noting that he wasn’t a licensed medical provider and had misrepresented the services he provided. The insurer said he needed to pay back $175,528 and would not be allowed to continue billing.

Williams had more than one National Provider Identifier, so he just switched numbers and kept billing Cigna. More than a year later, in May 2016, Cigna sent another letter, saying he now owed $310,309 for inappropriate payments. In total, the company paid him more than $323,000. Williams never gave any of it back.

In October 2017, Williams’ long run came to an end when he was arrested by the FBI. After a two day trial, a jury convicted Williams of four counts of health care fraud. He was sentenced him to a little more than nine years in federal prison and ordered him to pay $3.9 million in restitution to United, Aetna and Cigna.