A former executive of entities that provided payroll tax services to small businesses pleaded guilty Wednesday to conspiracy and making false statements for his role in a $110 million tax fraud.

Between 2002 and 2008, John D. Walker, 68, of San Antonio, maintained a management role in the firms known as professional employer organizations (PEOs), which he admitted were set up as part of a pyramid scheme.

“It's a significant tax scam when you're talking over $100 million,” said Steven A. McCollough, special agent of the IRS' Criminal Investigation division in San Antonio. “The coffers have been robbed of $100 million-plus.”

Prosecutors said the companies would claim they collected and remitted to the IRS employment payroll taxes for the small businesses when in fact they pocketed the money. McCollough said the executives of the PEOs squandered the money.