Authorities have determined that parking-lot employees stole more than $1.5 million from the Smithsonian at the museum's Udvar-Hazy Air and Space annex in Chantilly, much more than first estimated.
The new estimate came to light at a hearing Friday in federal court in Alexandria, where a lot attendant, Freweyni Mebrahtu, 46, of Sterling, was sentenced to two years and three months in prison.
When charges were announced last year, authorities said they believed the losses exceeded $400,000 but were unsure of the exact amount.
At Friday's hearing, Mebrahtu 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 two-thirds of the money Mebrahtu took in.
Going into Friday's hearing, authorities had estimated that Mebrahtu stole nearly $1.2 million, based on length of employment and how much she typically stole each month. But prosecutors accepted her assertion that she did not steal during the Muslim holy days of Ramadan, and revised the loss attributable to Mebrahtu to $895,000.
A second employee, Meseret Terefe of Silver Spring, Md., was sentenced to 20 months in prison after admitting to the theft of $487,000 in parking fees.
A third employee died awaiting trial, and an exact count was never determined, but court records show that authorities believe she stole more than $120,000.
Visitors to the Udvar-Hazy center typically pay a $15 parking fee. Court records show that Mebrahtu and other employees engaged in the scheme routinely unplugged machines that counted the vehicles entering the building, and that on a typical day Mebrahtu would fail to log in nearly 40 percent of the cars that came through her lane.
PMI is a major parking contractor in the D.C. region and holds numerous contracts, including one at Baltimore-Washington International Airport.
PMI officials did not return calls seeking comment Friday.
PMI continues to serve as the Smithsonian's parking contractor at Udvar-Hazy Center, said museum spokeswoman Claire Brown. The contract expires in April, and Brown said the museum will review at that time whether to select a new vendor.
Brown said changes were implemented after last year's arrests to make it impossible for thefts to occur in the same manner.