One officer was placed on leave Monday, one day after the incident. CDA said it will not release the names of the officers.
United Airlines CEO Oscar Munoz spoke Wednesday in an exclusive interview with ABC News about the passenger, who was bloodied as he was violently dragged off a flight at O'Hare International Airport.
Munoz called the incident "horrific" and promised to make changes in the future.
Dr. David Dao, 69, recovered Wednesday at a hospital, according to two Chicago attorneys representing him.
READ MORE: Who is Dr. David Dao?
Dao and Munoz had not spoken as of 11 a.m.
WATCH: MUNOZ INTERVIEW WITH ABC NEWS
Munoz said the incident was the result of a system failure. He said the world caught United at a bad moment and that it would never happen again.
He gave an apology in an interview with ABC News' Rebecca Jarvis in Chicago, as he responded to the international outrage prompted by video of Dao being pulled from his seat last Sunday and dragged by his hands down the aisle of a plane.
RAW VIDEO: UNITED PASSENGER DRAGGED OFF FLIGHT AT O'HARE
"The first thing to say is to apologize to Dr. Dao, his family, the passengers on that flight, our customers, our employees. That is not who our family at United is," Munoz said.
READ MORE: United Airlines Doctor Video - Moment-by-moment timeline of Flight 3411
New video shows Dao refusing to get off the flight, saying he needed to get home to see patients in the morning.
United was trying to get four passengers to leave the plane to make room for a flight crew.
Munoz initially called Dao "disruptive and belligerent." But he did an about-face days later, saying the doctor did nothing wrong.
"My initial words fell short of truly expressing what we were feeling. That's something that I've learned from. The expression of apology," Munoz said. "He was a paying passenger, sitting in our seat, in our aircraft. No one should be treated that way."
Munoz said he needs to give frontline managers better resources and policies, so they can use better common sense.
He also promised to review over-booking procedures and vowed to never again to use law enforcement to take a passenger off a boarded plane.
"To remove a booked, paid, seated passenger... We can't do that," Munoz said.
All customers on Flight 3411 Sunday are receiving compensation for the cost of their tickets, United said. United is offering compensation in the form that the passenger wants. Some people are getting a refund, others a travel voucher and still others air miles, depending on what they tell the airline they want.
United customers at O'Hare reacted Wednesday to the promised changes.
"I think that they'll follow through. They care about their customers. I hope they resolve the problem," said traveler.
"This isn't the worst thing that's happened before, for an airline," said Lanya Grammer. She "absolutely" thinks the problem can be fixed.
Many have called for a boycott of the airline. A protest was held Tuesday night at O'Hare. The Rainbow PUSH Coalition organized a protest for Wednesday afternoon.
In the first of what is expected to be a series of protests against United Airlines, Reverend Jesse Jackson and the Rainbow PUSH coalition are planning nationwide boycotts of United.
The boycott will be an effort to force United to diversify its board and its contractors.
Attorneys for Dao have filed court documents requesting all video, audio, reports and personnel files of the officers be preserved presumably for possible future litigation.
Editor's Note: United Airlines Flight 3411 was not overbooked. Our early reporting on the incident involving Dr. Dao makes reference to the flight being oversold because that was initially believed to be the cause for the removal of passengers. It has since been learned that passengers, including Dr. Dao, were removed to make room for four crew members.