A parking lot attendant who pleaded guilty to a scheme that stole nearly $487,000 in fees from lots at the Smithsonian Institution’s air and space museum in Chantilly was sentenced Friday to 20 months in prison, prosecutors said.

Meseret Terefe, 37, of Silver Spring, under-reported the number of vehicles using the lot during a three-year period starting in 2009, during which he stole as much as $4,500 a day. The money was collected from visitors, who had paid $15 per car to park at the Steven F. Udvar-Hazy Center, court files showed.

Terefe routinely stashed wads of cash into a duffel bag that he took home and used some of the proceeds to buy an interest in commercial property in Ethi­o­pia, prosecutors said. He also was ordered to make restitution during sentencing in United States District Court for the Eastern District of Virginia in Alexandria.

To mask the thefts, Terefe unplugged the electronic devices that counted cars as they passed through the pay lane he monitored or failed to hand drivers a windshield tag that helped track the fees paid, according to court files.

The company that handles the parking contract at the museum noticed losses and alerted the Smithsonian’s Office of the Inspector General, which investigated the case with the FBI.