LOS ANGELES (CBSLA.com/AP) – The CEO of United Airlines’ parent company says the airline is conducting its own investigation after police dragged a passenger from an overbooked United plane after he refused to give up his seat.

United Continental Holdings Inc. CEO Oscar Munoz said in a statement Monday that the incident late Sunday, which was caught on video, is “upsetting to all of us here at United.”

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United has said that the plane was overbooked and after fruitlessly asking for volunteers to leave the plane, employees selected four passengers at random to deplane. The airline requested law enforcement assistance when one man refused to leave.

Photos posted on social media appeared to show the unidentified passenger with visible injuries to his face, including a bloodied lip.

Munoz says he is reaching out to that man to “talk directly” to him. He apologized for having to “re-accommodate these customers” without elaborating.

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However, in an email sent to employees Monday, Munoz wrote, in part:

“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.”

The video shows the officers dragging the passenger down the aisle, as screaming can be heard.

Brian Sumers, a reporter for the travel industry website Skift, told KCAL9 Monday that decisions made regarding which passengers to bump are usually made based on flying status.

“If you’ve paid very little for your ticket and you very rarely fly that airline, you’re more likely to be bumped,” Sumers said.

Sumers said the airlines do have that right.

Meanwhile, the Chicago Department of Aviation said one of the involved police officers did not follow standard procedure and has been placed on leave.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)