Demonstrators protest United Airlines at Chicago’s O’Hare International Airport on Tuesday. The protest was in response to aviation security officers physically removing passenger David Dao from his seat and dragging him off a flight on Sunday. (Joshua Lott/AFP/Getty Images)

United’s efforts to contain a public relations crisis that has tarnished its image and led to calls for a boycott kicked into overdrive Wednesday with its chief executive appearing on national television to apologize, saying he felt “shame” when he saw video of the incident. The airline also promised refunds to the horrified passengers who watched as a fellow flier was dragged from his seat and down the aisle off the plane.

“This is not who our family at United is,” chief executive Oscar Munoz said in his first televised remarks since the incident Sunday. “You saw us at a bad moment. This can never, will never happen again on a United flight.”

When asked if the passenger, David Dao, was at fault for the actions that led to his removal from his Louisville-bound flight at Chicago’s O’Hare International Airport, Munoz said, simply: “No, he cannot be. He was a paying passenger sitting in his seat on our aircraft. No one should be treated that way.”

Meanwhile, lawyers for Dao filed an emergency bill of discovery in Cook County Circuit Court, asking that items in possession of United Airlines or the City of Chicago — which may contain information related to Sunday’s incident, including video footage of the boarding process, a passenger list and cockpit voice recordings from the flight — be preserved. A spokeswoman for the firms representing Dao said they will hold a news conference Thursday with a member of the Dao family. David Dao lives in Kentucky and was headed home when he was removed from the flight, they said.

Also Wednesday, two more officers involved in the incident were placed on administrative leave. The Chicago Department of Aviation placed one officer on paid leave Monday, pending an investigation. The officers’ names are not being released due to collective bargaining agreements, officials said.

Munoz’s appearance on ABC’s “Good Morning America” was the first time he has spoken publicly about the incident that has led to international backlash against the airline.

The incident, and the actions by officers who boarded the plane to remove Dao after he refused a last-minute request to give up his seat to a crew member, have become a rallying cry for every traveler who has ever felt mistreated by an airline. There have been calls for a boycott of United from as far away as China, where the story has stirred outrage because Dao is Asian. United officials said that race was in no way a consideration when they chose who would be removed from Flight 3411.

In the GMA interview, a contrite Munoz apologized to Dao, his family and the other passengers aboard the plane.

He also expressed regret for initial statements in the days following the incident that appeared to blame Dao. In a letter to United employees that was leaked to CNBC, Munoz said Dao was “belligerent.”

“My initial words fell short of truly expressing what I was feeling,” Munoz said Wednesday. “That is something that I’ve learned from.”

In pledging a full investigation into the matter, Munoz also suggested there will be changes in the way local law enforcement deals with passengers aboard United flights. When Dao refused to leave the flight voluntarily, police were called to remove him.

“The use of law enforcement aboard an aircraft has to be looked at very carefully,” Munoz said. “That is a policy that we absolutely have to look at.”

Munoz said United will publicly release the results of its internal investigation by April 30.

Videos shot by passengers aboard the flight show Dao screaming as he is dragged down the aisle of the plane and again a few minutes later when he returns to the plane. Dao’s face is bloody and his clothing mussed. When asked his reaction to seeing the footage, Munoz said “shame” was among the words that came to mind.

The incident has raised hopes among passenger-advocate groups such as and the National Consumers League that Congress will act on overhauls to make air travel more consumer-friendly.

The video has caught the attention of members of Congress, many of whom are frequent fliers. Nearly a dozen members have sent letters to United, officials at O’Hare and the Transportation Department demanding an explanation for why Dao was forcibly removed from the plane. Transportation officials said the agency’s Office of Aviation Enforcement and Proceedings is reviewing the matter. They noted that the flight was operated by one of United’s regional partners, Republic Airlines. D.C. Del. Eleanor Holmes Norton (D) has called for hearings into the matter.

Sen. Chris Van Hollen (D-Md.) said he is seeking support for a “Customers Not Cargo Act,” which would prohibit airlines from forcibly removing boarded passengers due to overbooking or airline staff seeking to fly as passengers.

“We were all shocked and outraged this week when United Airlines forcibly and brutally removed Dr. David Dao from Flight 3411,” Van Hollen wrote to his colleagues. “We should act immediately to ensure that airlines cannot force passengers who have already boarded to leave the plane to free up seats for others.”

New Jersey Gov. Chris Christie (R) also joined the fray, saying on CNN that he has asked the Trump administration to prevent airlines from overbooking flights until new guidelines are put into place.

But the Trump administration has so far expressed little desire to get involved. During a briefing Tuesday, press secretary Sean Spicer said that while the video was “troubling,” he dismissed calls for a federal investigation into what he said should be “a very local matter.”

There also have been calls for Munoz to step down from the job he has held since September 2015, but he dismissed the idea.

“I was hired to make United better and we’ve been doing that, and that’s what I’ll continue to do,” he said.