According to a May 12 letter made public by passenger advocacy group Flyers Rights this week, the Department of Transportation decided not to fine the airline. The agency found no evidence that United violated the passenger’s civil rights, nor any proof that he had been discriminated against on the basis of his race.

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The April incident went viral when a video was released showing 69-year-old David Dao being dragged off an overbooked flight. When United staff asked him to give up his seat for an airline crew member, Dao refused, and was dragged from his seat and down the aisle by airport security. He suffered a broken nose, a concussion, and lost two teeth.

Dao pressed charges against the airline, and Congress held a series of hearings investigating the state of airline travel. Following the decision made by the Department of Transportation, Paul Hudson, president of Flyers Rights, criticized the agency.

“For the Department of Transportation to conclude that United Airlines’ conduct did not warrant an enforcement action is a dereliction of duty,” he argued.

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For its part, United said in a statement that “this incident should never have happened and we are implementing all of the improvements we announced in April, which put the customer at the center of everything we do.”