United Airlines CEO Oscar Munoz sent a letter to employees Monday night addressing the incident where a passenger was forcibly removed from a plane the day before.

In the letter, obtained by CNBC, Munoz included a summary of what happened from United Airlines’ perspective and called the passenger “disruptive and belligerent,” saying he left crew “no choice but to call Chicago Aviation Security officers to assist in removing the customer from the flight.”

The passenger was physically removed from his seat on an overbooked flight Sunday by aviation security officers. Video from the incident, which quickly went viral, showed the man screaming and his face bloodied as other passengers yelled at officers to stop removing the man. Police continued to drag the passenger down the aisle of the plane by his arms.

In the statement to employees, Munoz said he “emphatically” stood behind all crew.

Dear Team,

Like you, I was upset to see and hear about what happened last night aboard United Express Flight 3411 headed from Chicago to Louisville. While the facts and circumstances are still evolving, especially with respect to why this customer defied Chicago Aviation Security Officers the way he did, to give you a clearer picture of what transpired, I've included below a recap from the preliminary reports filed by our employees.

As you will read, this situation was unfortunately compounded when one of the passengers we politely asked to deplane refused and it became necessary to contact Chicago Aviation Security Officers to help. Our employees followed established procedures for dealing with situations like this. While I deeply regret this situation arose, I also emphatically stand behind all of you, and I want to commend you for continuing to go above and beyond to ensure we fly right.

I do, however, believe there are lessons we can learn from this experience, and we are taking a close look at the circumstances surrounding this incident. Treating our customers and each other with respect and dignity is at the core of who we are, and we must always remember this no matter how challenging the situation.

Oscar

Summary of Flight 3411

- On Sunday, April 9, after United Express Flight 3411 was fully boarded, United's gate agents were approached by crewmembers that were told they needed to board the flight

- We sought volunteers and then followed our involuntary denial of boarding process (including offering up to $1,000 in compensation) and when we approached one of these passengers to explain apologetically that he was being denied boarding, he raised his voice and refused to comply with crew member instructions.

- He was approached a few more times after that in order to gain his compliance to come off the aircraft, and each time he refused and became more disruptive and belligerent.

- Our agents were left with no choice but to call Chicago Aviation Security Officers to assist in removing the customer from the flight. He repeatedly declined to leave.

- Chicago Aviation Security Officers were unable to gain his cooperation and physically removed him from the flight as he continued to resist -- running back onto the aircraft in defiance of both our crew and security officials.

Witnesses on board the plane said the man explained to crew members that he couldn’t leave because he was a doctor and had to get to work at a hospital the next day.

United Airlines had already been feeling the heat from travelers following an incident in March in which two young girls were stopped from boarding a plane for wearing leggings. United said since the girls were flying as “pass riders” through a discounted program for relatives of airline employees, the attire didn't comply with the dress code.