United Airlines CCTV shows moments before dragging drama

New surveillance video of the United Airlines incident when a man was brutally dragged off a plane has been released, shedding new light on the saga.

NBC News obtained the footage and audio recordings from the boarding gate and the plane. Statements from security officers involved in the incident have also been released.

Dr David Dao, 69, was dragged, with a bloodied face and apparently unconscious, down the aisle of the United Airlines plane by airline security on April 9, when the flight was overbooked and he refused to leave his seat.

CCTV video shows Dr Dao boarding the flight, originally bound for Louisville, Kentucky.

Audio recordings then reveal the call boarding gate workers made, asking airport security to come onto the plane and remove Dr Dao.

"Were they drinking, were they doing anything like that?" the security person asks.

"No it's something with an oversold, involunteer [sic] something like that," the boarding gate caller says.

"Oh you guys overbooked the flight? This is a departing flight?" security asks.

"Yeah," the caller says.

Surveillance footage shows an aviation security car arrive at the plane, then guards board the plane.

Dr Dao's wife is then seen hurrying out the boarding gate, before returning back to the plane.

While that is happening, passengers in the cabin are filming as security staff drag Dr Dao from his seat.

The CCTV footage shows an ambulance arrive outside the plane, as passengers leave through the board gate.

Three security officers involved filed incident reports with the Chicago Department of Aviation, saying they were "under duress" and feared losing their jobs.

Officer James Long, who first tried to pull Dr Dao, wrote that he had his arms "folded tightly" but when they tried to move him he "started swinging his arms up and down with a closed fist".

But Dr Dao's lawyer says it's utter nonsense. "He's a pussycat, and there's video showing that."

Passengers' cellphone footage shows Dr Dao was not violent.

The new documents also show Officer Long had been suspended weeks earlier for insubordination, NBC reports.

Officer Long says after pulling Dr Dao back to the boarding gate, he got off the floor and ran to get back to the plane.

United Airlines chief executive Oscar Munoz apologised, saying: "[The incident] has elicited many responses from all of us: outrage, anger, disappointment.

"I share all of those sentiments, and one above all: my deepest apologies for what happened."

"Like you, I continue to be disturbed by what happened on this flight and I deeply apologise to the customer forcibly removed and to all the customers aboard. No one should ever be mistreated this way."

He says the company takes full responsibility and "will work to make it right".