The small grassy hill and handful of hedges around the United States Post Office in Waverly, Maryland, isn’t much to look at. But federal prosecutors say that for branch manager Richard L. Wright III, the grounds were a cash cow.

Authorities filed criminal complaints against Wright, 46, of Essex, Maryland, and Kimberly Parnell, 43, the manager of the Pikesville Post Office branch, accusing them of collectively taking tens of thousands of dollars in kickbacks from landscape and janitorial contractors who had been paid based on bogus invoices.

From 2007 to February 2013, authorities say, a landscape contractor at the Waverly branch had been paid $419,000 for work that had been partially completed or, more often, not done at all.

Court records show that the landscape contractor began working as an FBI source earlier this year.