Federal officials have decided not to punish United Airlines over an infamous incident in which a passenger was dragged off an overcrowded plane.

The Transportation Department said it found no evidence that United violated the passenger’s civil rights and not enough evidence that it violated rules regarding bumping passengers.

A department lawyer told United about the decision in a May 12 letter, but neither the agency nor the airline made the matter public. An advocacy group, Flyers Rights, released the letter today after obtaining it through an open-records request.

On April 9, airport security officers in Chicago dragged 69-year-old David Dao from a United Express plane. The airline said it needed room for four employees who were traveling to staff a flight the following morning.