Lawyers for David Dao, the doctor forcibly dragged off a United Airlines plane, filed an emergency request with an Illinois state court on Wednesday to require the carrier to preserve video recordings and other evidence related to the incident.

Citing the risk of “serious prejudice” to their client, the lawyers want the airline and the City of Chicago, which runs O’Hare International Airport, to preserve surveillance videos, cockpit voice recordings, passenger and crew lists and other materials related to United Flight 3411.

United says passengers on United Express Flight 3411 are getting compensation equal to the cost of their tickets, according to The Associated Press. United spokeswoman Megan McCarthy said Wednesday that the passengers can take the compensation in cash, travel credits or miles.

The filing with the Cook County Circuit Court likely presages an eventual lawsuit against United for the April 9 incident, where Dao was snatched from the seat he had paid for, and was dragged by his hands on his back off the parked plane, which had been bound for Louisville, Kentucky.

Dao is scheduled to hold a press conference Thursday morning, his legal team said.

United Chief Executive Officer Oscar Munoz on Wednesday apologized to Dao and said the company would no longer use law enforcement officers to remove passengers from overbooked flights. A video of Dao being dragged off the flight, bleeding, went viral this week, causing global outrage.

Much of the uproar stemmed from Dao’s status as a paying passenger who was being removed, against his will, to make room for additional crew members on the overbooked flight.

Three security officers have been placed on leave after the incident, according to the Chicago Department of Aviation. Their names have not been released.