A 15-year veteran of the Prince George's County Revenue Authority resigned Wednesday after learning that he was at the center of an investigation into thousands of dollars skimmed from the parking garage where he worked, county authorities said.

The total amount missing from the garage was "in the ballpark of $100,000," according to a source familiar with the probe, who spoke on condition of anonymity because of the ongoing investigation.

Authorities have not released the employee's name because he has not been charged. They said they believe that the man was acting alone.

Jim Keary, a county spokesman, said that the Revenue Authority, a quasi-governmental agency that operates parking facilities and collects money from parking violations, had instituted tighter financial controls in 2004.

Last week, a monthly audit tipped off authorities to the missing money. The money had been taken during the second half of June and the first half of July, Keary said.

Police would not identify the garage.

The investigation comes as the Maryland state prosecutor's office is looking into the actions of two other former Prince George's officials.

Those men are under investigation for allegedly seeking $250,000 in bribes in exchange for awarding a $1 million security contract, according to three government officials with knowledge of the case.