The Udvar-Hazy Air and Space Museum, Chantilly, Va. (Jeffrey Porter for The Washington Post)

After he spent a shift collecting fees at the Udvar-Hazy Center in Chantilly, parking booth attendant Meseret Terefe stuffed a bundle of the cash into a red duffel bag and headed for home one day in June, federal prosecutors said.

The theft was just one of many in an alleged three-year scam that was as lucrative as it was simple. Terefe and two other attendants netted at least $400,000 by unplugging the machines that counted cars at the Smithsonian’s National Air and Space Museum annex and taking those visitors’ $15 parking fees, according to federal prosecutors in Virginia.

On some days, Terefe, 36, of Silver Spring, and Freweyni Mebrahtu, 45, of Sterling, took more than $4,000, federal officials said in court papers. The third attendant, Genete Yigzu, 46, of Alexandria, allegedly grabbed as much as $2,000 on a single day.

All three were arrested Saturday after their shifts at the Udvar-Hazy Center and were charged in federal court in Alexandria with embezzling money from the Smithsonian. Each faces a maximum of 10 years in prison if convicted.

“During a time of challenging budgets, the alleged theft of hundreds of thousands of dollars from the Smithsonian, a revered American institution, is extremely troubling,” said Neil H. MacBride, the U.S. attorney for the Eastern District of Virginia.

The three began stealing parking fees in April 2009, shortly after their employer, Parking Management Inc. (PMI), took over managing the 2,000-space lot, prosecutors said in court papers. Prosecutors said a confidential informant tipped off authorities that the attendants were stealing money in October 2011.

Cameras installed by law enforcement in the attendants’ booths captured all three unplugging boxes that counted the number of vehicles passing into the lot, according to affidavits filed in court. The technique allegedly allowed them to under-report the number of paying customers — sometimes by hundreds a day.

For instance, law enforcement determined that there were 261 more vehicles than were reported passing Terefe’s booth during his shift on May 26, 2012, according to one affidavit.

The cameras also captured Terefe filling his duffel bag with cash on two occasions, according to court papers. At the time, Terefe was making $11 an hour and was working at the lot only two days a week. His annual salary was less than $10,000 a year.

Authorities believe Terefe used the cash he stole to buy a 2012 Toyota Rav4, but court documents do not detail what the other attendants did with the money they allegedly stole.

An attorney for Mebrahtu did not return a call for comment. Attorneys for the other two defendants have not been appointed yet.

The Udvar-Hazy Center, which opened in 2003, had about 1.2 million visitors last year. Its aviation-related displays include a Lockheed SR-71 Blackbird and the well-known Enola Gay, the B-29 that was used to drop an atomic bomb on Hiroshima during World War II.