Authorities have now determined that parking-lot employees stole more than $1.3 million from the Smithsonian at the museum's Air and Space annex in Chantilly.
The new estimate came to light at a hearing Friday in federal court in Alexandria where one of the lot attendants was sentenced to more than two years in prison.
When charges were first announced last year, authorities believed the losses exceeded $400,000 but were unsure of the exact amount.
At Friday's hearing, former attendant Freweyni Mebrahtu (freh-WAY'nee meh-BRAH'-too) of Sterling admitted she alone stole $895,000 over a three-year period.
She said she did so at the urging of supervisors with parking contractor PMI, who demanded a share of the money.
Mebrahtu said she stole throughout her employment, except during the Muslim holy days of Ramadan.
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