After two days of conflicting corporate statements, falling stocks and swelling outrage, United Airlines entered full-scale mea culpa mode Tuesday afternoon, as its chief executive announced an internal investigation into a Sunday-evening flight in which a man was dragged violently from his seat so a crew member could have it. "I continue to be disturbed by what happened on this flight," United chief executive Oscar Munoz wrote in a statement. "I deeply apologize to the customer forcibly removed and to all the customers aboard. No one should ever be mistreated this way." "We are going to fix what's broken so this never happens again," Munoz wrote — promising a report on the beleaguered airline's policies on calling police, transferring crew and "how we handle oversold situations." It was the latest in a flurry of attempts from the airline to defuse a public relations crisis. Hours earlier, according to USA Today, a United spokesperson had backed off the company's initial claims that the flight was "overbooked" — rather than disrupted to transport off-duty crew. And before that, Munoz had defended his employees, saying the passenger, who refused to give up his seat, was belligerent. The battered and bloodied man was dragged back to the terminal at Chicago's O'Hare International Airport. One of the officers involved in the incident was placed on leave pending an investigation. But international outrage continued Tuesday, with United's stock price falling, memes exploding and disturbing videos of the incident shared across the world. RELATED CONTENT: Social media offers savage new United Airlines mottos The White House also weighed in. Press secretary Sean Spicer called the videos "troubling" but dismissed calls for a federal investigation into what he said should be "a very simple local matter." The U.S. Department of Transportation also said it was looking into the matter. In China, where United bills itself as a top carrier, tens of millions of people have read or shared a report that the passenger claimed he was targeted for being Chinese. Many there are now echoing calls in the United States for a boycott. "Like you, I was upset to see and hear about what happened last night," United chief executive Munoz wrote in a memo to the company — while defending the crew's conduct on the Louisville-bound plane as "established procedures." "I deeply regret this situation arose," Munoz wrote, according to the Associated Press. But: "I want to commend you for continuing to go above and beyond to ensure we fly right." United's brief initial response to the incident — that Flight 3411 was "overbooked" and police were called after a man "refused to leave the aircraft voluntarily" — has now given way to a more detailed story told by witnesses, police, the Chicago Department of Aviation and Munoz himself. It's a story that has shaken a global air carrier worth billions of dollars _ and one that people around the world can find nothing right in at all. In early trading Tuesday morning, United had lost hundreds of millions of dollars in market capital, according to MarketWatch. "How to make a PR crisis a total disaster," was the headline on a CNN story about United's response to the incident. Flight 3411 had finished boarding Sunday evening, according to a summary attached to Munoz's letter, when "gate agents were approached by crew members" who needed seats. Passengers were initially offered money if they gave up their seats, but no one volunteered. If the off-duty crew had not been able to get to Louisville that night, a United spokesman told the Louisville Courier Journal, another flight might have been canceled. So the airline invoked what it describes as its "involuntary denial of boarding process." Which is where the trouble started. When passengers expecting to take off for Louisville learned that some of them would be forced to leave, the mood on the jet quickly soured, Tyler Bridges told the Washington Post. link rel="stylesheet" type="text/css" href="http://www.tampabay.com/specials/2015/graphics/macros/css/base.css"> Bridges and his wife were on the last leg of a journey home from Japan, he said. Before takeoff, an airline supervisor brusquely announced: "This flight's not leaving until four people get off." And since no passenger was willing, United chose for them. A young couple "begrudgingly got up and left," Bridges recalled. The third evictee complied, too. But when the crew approached what Chicago police told NBC was a 69-year-old Asian man in a window seat, he refused. "He says, 'Nope. I'm not getting off the flight,'" Bridges said. "'I'm a doctor and have to see patients tomorrow morning.'" United said crew members apologetically told the man to leave, several times, "and each time he refused and became more and more disruptive and belligerent." "He wasn't cussing, but he was yelling and he was upset," Bridges said. "He said, more or less, 'I'm being selected because I'm Chinese.'" (Another witness on the plane said the man was originally from Vietnam, according to the BBC.) So the airline called the Chicago Department of Aviation, which handles security at O'Hare. An officer boarded. Then a second and a third. By then, Bridges and another passenger were taking video on their cellphones - footage that would soon be seen by millions. As officers leaned over the lone holdout in a window seat, passengers across the aisle sympathized with him. "Can't they rent a car for the pilots?" a woman asks in the videos. Out of frame, the man suddenly screams. One of the officers quickly reaches across two empty seats, yanks him up and pulls him into the aisle. "My God!" someone yells — not for the first time. The man's face smacked an arm rest as the officer pulled him, according to witnesses and police. "It looked like it knocked him out," Bridges said. "His nose was bloody." In any case, in the video, the man goes limp after hitting the floor. Blood trickling from his mouth, his glasses nearly knocked off his face, he clutches his cellphone an officer drags him by both arms down the aisle. "Like a rag doll," as one witness wrote on Twitter. "What are you doing?" someone asks in the video, as the man slides past. "No! This is wrong." When the man was gone and all four seats were free, Bridges said, the four stranded crew members boarded and took them. They were jeered, he recalled: "People were saying you should be ashamed to work for this company." Had the plane left then, that might still have been enough to spark the fury that would come when Bridge's video went public. But a few minutes later, the man ran back onto the plane. "He continued to resist," United wrote in its summary, "running back onto the aircraft in defiance of both our crew and security officials." In Bridge's second video, the man appears frantic. His clothes are still mussed from the dragging, his mouth bloody. "I have to go home," he keeps saying. "I have to go home." A group of high school students stood up and left the plane at that point, Bridges said. "They don't need to see this anymore," their escort explained to other passengers. The airline eventually cleared everyone from the plane, and did not let them back on until the man was removed a second time - in a stretcher. Bridges and his wife got home to Louisville a few hours later that night. On Tuesday, the Louisville Courier-Journal identified that passenger as David Dao, a doctor from Elizabethtown who has had a troubled history in Kentucky. The newspaper reports that Dao was arrested in 2003 and eventually convicted of drug-related offenses after an undercover investigation. Documents filed with the Kentucky Board of Medical Licensure allege Dao "was involved in fraudulent prescriptions for controlled substances and was sexually involved with a patient who used to work for his practice and assisted police in building a case against him." Dao, who went to medical school in Vietnam in the 1970s before moving to the U.S., was convicted of multiple felony counts of obtaining drugs by fraud or deceit in November 2004 and was placed on five years of supervised probation in January 2005. He surrendered his medical license the next month. The Kentucky Board of Medical Licensure permitted Dao to resume practicing medicine in 2015 under certain conditions, according to the Courier-Journal. News of the incident dominated news shows and social media — with people live-Tweeting alleged overbooking incidents Tuesday. Videos tagged "United Related" (ironically or not) became basically the only thing visible on Reddit's ultra-popular videos sub-forum. The chief executive at the center of the storm issued a public apology Monday "for having to re-accommodate these customers" - phrasing that was widely derided in a meme-storm. United pointed to unspecified law enforcement for everything seen in the video, which led Chicago police to issue a statement claiming the injured man "fell." But late Monday afternoon, the Chicago Department of Aviation - a different agency - said it had suspended one of the officers in the video: "The incident on United flight 3411 was not in accordance with our standard operating procedure and the actions of the aviation security officer are obviously not condoned by the Department," the agency said in a statement. "That officer has been placed on leave effective today pending a thorough review of the situation."