Self-confessed tax scam mastermind Harriette Walters was sentenced to 17-and-a-half years in prison Tuesday, nearly one year for every year she stole from the D.C. tax office in the largest embezzlement scheme in city history.

U.S. federal Judge Emmet Sullivan said the maximum of 18 years was “eminently reasonable,” but that he subtracted six months because she cooperated with authorities.

Walters was a mid-level manager in D.C.’s Office of Tax and Revenue who manipulated a broken property tax refund system for two decades, draining $48 million from city coffers. In jail since her 2007 arrest, she pleaded guilty last September.

In October, she met with auditors hired by the D.C. Council and explained how she was able to work her scam and steal so much for so long.

“If you let me into my office,” Walters told them, “I guarantee I could get each of you a check.”

Prosecutors had asked for an 18-year-sentence.

“One year for every year she stole from our great city,” Assistant U.S. Attorney Timothy Lynch said.

A dozen of Walters’ conspirators, mostly family and friends, already have been sentenced for their roles in the scam.