A film producer who was sitting next to a man whose erratic behaviour caused a JetBlue flight into a premature landing has posted a dramatic account of the experience.

Cassian Elwes, who spent much of the New York to Los Angeles flight next to a man he identifies as Marco, describes how he tried to keep the man calm as the plane was diverted to Denver.

His account paints a sympathetic portrait of a troubled former marine who was apparently receiving treatment for a psychological disorder.

Cellphone footage shows the man being escorted from the plane at Denver in handcuffs. Video footage obtained by ABC7 also showed the man being escorted from the plane.

"I want to write this all down before I forget it even though its 3.45am," Elwes wrote on Twitter on Monday morning, referring to Pacific time. "I just got home. Tonight I took the 9pm jet blue from ny to lax."

What followed was a gripping blow-by-blow account of the ordeal, posted over a two-hour period.

After boarding Elwes had approached his seat – "20f a window seat I had specifically booked" – to find "a youngish looking guy", "quite burly white crew cut lots of tattos [sic]".

Hey that's my seat man I said. A quick drawling fuck you its mine now was the response I sat down next to him mumbling 'charming'.

— cassian elwes (@cassianelwes) August 20, 2012

Elwes took the seat next to the man, but then moved to the row directly behind to allow a couple to sit next to one another. It was around an hour into the flight when the man began to behave oddly, according to Elwes.

Hoodie wants to get up. he walks to the back & stands in the galley for 10 mins just staring at the metal wall. The stewardesses ignore him

— cassian elwes (@cassianelwes) August 20, 2012

The man stood up again, this time walking to the front of the plane. Elwes said he was "really not sure that its a good idea that he's hanging around the front where all the buttons are for the doors", and notices "some sort of exchange with him and a lady who's just come out of the loo".

It is then that the man's behaviour appears to deteriorate, as he begins "staring at some guy not saying anything for five minutes like he wants to fight someone".

Elwes, concerned, asks if there is an air marshal onboard but is told that they cannot identify themselves. An air steward calls the captain, however, and learns that there is another off-duty marshal on the plane.

The japanese couple get up and go stand in the back.The plane is totally full & there is nowhere else for them to sit.The off duty guy comes

— cassian elwes (@cassianelwes) August 20, 2012

He sits down next to hoodie and they exchange a few words. I'm right behind and now hoodie starts shouting at the guy fuck you many times

— cassian elwes (@cassianelwes) August 20, 2012

As the man's behaviour continued, the air stewards asked passengers if anyone would volunteer to sit next to the individual. Elwes said the off-duty air marshall had by now taken the aisle seat, leaving the middle one free, with the couple unwilling to return.

Elwes, who said he was "feeling quite guilty for switching with the japanese couple in the first place", volunteered to sit next to the man.

I sit. The smell of alcohol is incredible. Do like movies. fuck you. Do you go to films. Fuck you. Do you write at all. Fuck you.Yes he says

— cassian elwes (@cassianelwes) August 20, 2012

Elwes attempted to distract Marco by talking about films, and where he grew up. At one point the man "swigs from" a canister filled with little green pills. Elwes said he told the air marshal, "I think I can keep him talking for the next 2 hrs", seemingly managing to calm the man as they talk about his tattoos and the possibility of turning one of his short stories into a movie. However the captain says the plane is being diverted due to a "small problem on board".

The plane starts a rapid descent. The air marshal whispers to me get up when we start taxi-ing. The cops will come on ,get out of the way

— cassian elwes (@cassianelwes) August 20, 2012

Marco is still repeating don't forget me as we land and taxi. Wow I hate la he says again. I need to go to the bathroom I say and get up

— cassian elwes (@cassianelwes) August 20, 2012

The captain comes on and asks everyone to remain seated. A precaution he says. A few minutes later 2 policemen come in . Marco stands up.

— cassian elwes (@cassianelwes) August 20, 2012

With not much fuss they handcuff him and lead him down the aisle and out of the plane. Its silence. The 2 stewardesses come up and thank me

— cassian elwes (@cassianelwes) August 20, 2012

A spokeswoman for Denver International Airport confirmed that the plane was met by authorities in Denver and a passenger removed. Denver police and FBI agents responded to the scene, the spokeswoman said. JetBlue said the flight was rerouted for a customer service reason.

Elwes said a woman passenger accused Marco of groping her on the plane and said she would press charges. Elwes also gave a statement to police in Denver before the plane continued onto Los Angeles. "I write that I used to be william morris agent and I've dealt with difficult people before and really this guy wasn't that difficult," he said, but is left reflecting on what will become of him.

Now I can't help feeling bad for marco. Its a federal offence to make a plane land and the charges from the woman will probably be assault

— cassian elwes (@cassianelwes) August 20, 2012

After Marco is removed from the plane Elwes said he began to "replay the whole thing in my mind". "What's the message what's the point," he wonders.

I realize the point is these wars are fucking with our children's minds. A whole generation is being sent home screwed up.

— cassian elwes (@cassianelwes) August 20, 2012

Elwes added that he found one of Marco's pills on the floor. With the help of a fellow passenger he discovered that it is a drug used to treat "bi-polar anxiety".

During their conversation Elwes had asked Marco to write down his email address, after Marco said his story should be made into a movie. With Marco escorted off the plane, repeatedly asking Elwes not to forget him as he left, Elwes said he opened the piece of paper to find a note.

'We all love the ones we hate. Blood. Lust. I was born in queens. We all lose hope'. Marco I won't forget you I promise.

— cassian elwes (@cassianelwes) August 20, 2012

Read back Elwes's account in full @CassianElwesRead a Storify of Elwes's tweets by Jen Chung from Gothamist.

© Guardian News and Media 2012

[JetBlue airline via Christopher Parypa / Shutterstock.com]