CHICAGO—The man dragged from a full United Express flight by airport police in Chicago is a Kentucky physician who was convicted more than a decade ago of felony charges involving his prescribing of drugs and spent years trying to regain his medical license.

But while the passenger’s unflattering history quickly became the focus of attention, there’s no indication that his past influenced how he was treated or that the airline or police were aware of his background. And it’s unlikely that officials would have known anything about him other than basic information such as his name and address, if that.

Meanwhile, the airline issued a more contrite apology Tuesday and pledged to conduct a review of the company’s practices that led to the events at O’Hare Airport.

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“No one should ever be mistreated this way,” said Oscar Munoz, chief executive of United’s parent company.

A person with knowledge of the Sunday evening flight who was not authorized to publicly release the information told The Associated Press that the passenger was David Dao, 69, of Elizabethtown, Kentucky. Dao did not return messages from the AP.

Screaming can be heard on the videos, but nowhere is Dao seen attacking the officers. In fact, he appears relatively passive both when he was dragged down the aisle of the jet and when he is seen standing in the aisle later saying quietly, “I want to go home, I want to go home.”

When cellphone videos taken by other passengers first emerged, they generated widespread sympathy for Dao and sharp criticism of the airline.

Twitter users used the platform to poke fun at the airline’s tactics.

“We overbooked but you pay the price,” “We Put The Hospital In Hospitality” and “We’ll drag you all over the world” are among the faux slogans being offered up on social media under #NewUnitedAirlinesMottos.

The incident risks a backlash against United from passengers who could boycott the airline as the busy summer travel season is about to begin. For Chicago, it is another public relations nightmare, adding to its reputation as a city unable to curb a crime wave in some neighbourhoods, which U.S. President Donald Trump has highlighted with critical tweets.

Munoz initially released a statement saying that United wanted to talk to the man. But hours later, he later began defending his employees, describing the passenger as “disruptive and belligerent.”

That comment suggested that Dao’s actions could be examined closely by United and the Chicago Aviation Department, though it remains unclear what role Dao’s past might play in those investigations.

Munoz then issued another statement describing the removal as “truly horrific.” He planned to review policies for seeking volunteers to give up their seats, for handling oversold situations and for partnering with airport authorities and local law enforcement.

The company expected to share results of the review by April 30.

According to records from the Kentucky Board of Medical Licensure, Dao went to medical school at the University of Medicine of Ho Chi Minh City in Vietnam, graduating in 1974. He was licensed in Kentucky with a specialty in pulmonary disease.

His legal troubles started in 2003, when his medical license was suspended after an undercover sting operation at a Louisville motel for allegedly writing fraudulent prescriptions.

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According to the documents, the licensing board had learned that Dao had become sexually interested in a patient and hired the patient as his office manager. That man later said he quit his job because Dao “pursued him aggressively” and arranged to provide him with prescription drugs in exchange for sex.

Dao was ultimately convicted in late 2004 of several counts of obtaining drugs by fraud or deceit and was placed on five years of supervised probation and surrendered his medical license.

His longtime effort to get his license back finally succeeded in 2015, when the licensing board allowed him to practice medicine again.

Airport officials have said little about the Sunday’s events and nothing about Dao’s behaviour before he was pulled from the jet that was bound for Louisville, Kentucky. Likewise, the Aviation Department has said only that one of its employees who removed Dao did not follow proper procedures and has been placed on leave.

No passengers on the plane have mentioned that Dao did anything but refuse to leave the plane when he was ordered to do so.

On Monday, Chicago Mayor Rahm Emanuel called the altercation “completely unacceptable” and praised Aviation Commissioner Ginger Evans for taking “swift action.” He promised that a city investigation would “ensure nothing like this ever happens again.”

Sunday night’s confrontation stemmed from a common air travel issue — a full flight. United was trying to make room for four employees of a partner airline, meaning four people had to get off.

At first, the airline asked for volunteers, offering $400 and then when that did not work, $800 per passenger to relinquish a seat. When no one voluntarily came forward, United selected four passengers at random.

Three people got off the flight, but the fourth said he was a doctor and needed to get home to treat patients on Monday. He refused to leave.

Three men, identified later as Aviation Department police officers, got on the plane. Two officers tried to reason with the man before a third came aboard and pointed at the man “basically saying, ‘Sir, you have to get off the plane,’” said Tyler Bridges, a passenger whose wife, Audra D. Bridges, posted a video on Facebook.

One of the officers could be seen grabbing the screaming man from his window seat, across the armrest and dragging him down the aisle by his arms.

Other passengers on Flight 3411 are heard saying, “Please, my God,” “What are you doing?” “This is wrong,” “Look at what you did to him” and “Busted his lip.”

“We almost felt like we were being taken hostage,” Bridges said. “We were stuck there. You can’t do anything as a traveller. You’re relying on the airline.”

With files from Bloomberg