The lawyer representing David Dao, the passenger violently dragged off a United Airlines flight April 9, said he is preparing to file a lawsuit against United for using “unreasonable force and violence” against the passenger.

Attorney Tom Demetrio said in an April 13 press conference in Chicago that Dao was discharged April 12 from a hospital, where he was treated for a “significant concussion, serious broken nose and injuries to the sinuses” all suffered during the incident in which Dao was dragged from an aircraft after being involuntarily bumped from United Express flight 3411 as it awaited to depart Chicago O’Hare for Louisville, Kentucky.

Demetrio said he is conducting due diligence ahead of filing a lawsuit, adding there will be a court hearing April 17 in Chicago regarding the preservation of evidence related to the case. United is primarily responsible, he said, but indicated other parties could also be implicated in a lawsuit.

These could include the City of Chicago, which employed the Chicago Department of Aviation law enforcement officer who dragged Dao down the aisle of the Embraer E170 aircraft, he said. Demetrio also indicated he believes a flight’s captain is responsible for everything that happens on the aircraft. The flight 3411 pilots are employees of Republic Airways Holdings, which operated the flight under contract with United.

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“Here’s the law. It’s real simple … Under no circumstances can [a bumped passenger be removed from an aircraft] with unreasonable force and violence,” Demetrio said, adding that United has a responsibility “to provide protection and safety to fare-paying passengers. That was not done in this case. I would defy anyone to suggest there was not unreasonable force and violence used.”

Demetrio cast the incident, which has reverberated globally, as part of a “culture” of the way airlines treat passengers. “For a long time, airlines—United in particular—have bullied us,” he said. “They have treated us less than we deserve.” Demetrio said over the last several days he has heard “hundreds of tales of woe of mistreatment from United.”

Demetrio said he hopes the lawsuit will lead to an “international discussion” about how airline passengers are treated. “We’re going to be vocal about the whole subject of what we as a society believe passengers are entitled to,” he said. “Are we going to be treated like cattle and bullied? … There is a culture of disrespect and rudeness. Rudeness and bullying customers has gone the next step to physical.”

Demetrio took United CEO Oscar Munoz to task for providing a “couple versions” of his reaction to the incident. He also noted that Munoz “hesitated” when asked in an ABC News television interview whether Dao was partially to blame for the incident before answering that the passenger was not to blame. “The public relations problem they have isn’t just limited to this video” of the incident, Demetrio said.

Demetrio and Dao’s daughter, Crystal Dao Pepper, who also appeared at the Chicago press conference, said neither Munoz nor United staff had reached out to Dao or his family, contradicting Munoz’s statement that he and the airline have tried to contact the passenger to apologize directly. “We were horrified and shocked and sickened” by the incident, Pepper said.

A United spokesperson said in an emailed statement that “Munoz and the company called Dr. Dao on numerous occasions to express our heartfelt and deepest apologies.”

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“This horrible situation has provided a harsh learning experience from which we will take immediate, concrete action,” the United spokesperson said. “We have committed to our customers and our employees that we are going to fix what’s broken so this never happens again. First, we are committing that United will not ask law enforcement officers to remove passengers from our flights unless it is a matter of safety and security. Second, we’ve started a thorough review of policies that govern crew movement, incentivizing volunteers in these situations, how we handle oversold situations and an examination of how we partner with airport authorities and local law enforcement. Third, we will fully review and improve our training programs to ensure our employees are prepared and empowered to put our customers first. Our values—not just systems—will guide everything we do. We’ll communicate the results of our review and the actions we will take by April 30.”

Aaron Karp