A party goer who unknowingly filmed a fight where a teenager was stabbed to death on a dance floor said she had “no idea” what she was about to catch on camera.

Charlie Cosser was fatally stabbed in the chest at the outdoor event called “BalFest” – attended by around 100 people at a farmhouse in Warnham, West Sussex, on July 23 last year.

A teenager, who was 16 at the time, is on trial accused of Charlie’s murder.

The prosecution allege the fatal injuries took place when a fight broke out between him, Charlie, and two other boys on the dance floor after the defendant and his friends were asked to leave the party.

Party guest Megan Roberts told Brighton Crown Court how she began filming because she liked the song, Toxic by Britney Spears, that was playing, before she realised what was going on.

Ms Roberts’ video footage played to jurors showed revellers just before midnight on July 22 dancing under disco lights in a marquee.

A fight is then visible in the background and the recording shortly ends.

Asked why she took the video on Tuesday, Ms Roberts said: “I believe I liked the song that was playing… it was to do with music, I had no idea what I was about to catch on film.

“I think I was just filming (my) friendship group.

“I didn’t realise what I happened to be filming.”

Ms Roberts said she had come to realise a lot of people at the party were younger than her and her friends, aged between 16-18, and the group decided to leave the party soon.

She said shortly after filming the video, a DJ announcement was made that the police had been called and the party was over.

At the end of the night on the way back to her car, Ms Roberts also described how the atmosphere felt busy with people leaving and said you could feel something bad had happened, adding: “You could feel it when you were there, I knew something had happened but I didn’t know what.”

She had heard someone had been stabbed but said: “I didn’t actually really believe that could have happened.”

Other party goers recalled to the court seeing a teenager lying down, covered in blood.

Guest Harriet West described how she walked over to a high-vis man acting as security to ask about leaving the party when the police were on the way, but “just walked away” as she saw a boy on the ground by him.

She said: “He didn’t have a T-shirt on and he had blood all over his chest.

“I just left. The man in the high-vis was going onto his knees.”

A friend of the defendant, also at the party, told the court he believed he saw a motionless Charlie being helped by two other people coming out of the marquee.

He told jurors: “I saw they were dragging him over, to the point I went over because I was concerned.

“They laid him down and there was blood all over his stomach.

“I told people to call an ambulance very quickly.”

Meanwhile, another party goer, Amelia Richards, told jurors that earlier in the night she had seen a group of three boys wearing dark tracksuits as she was walking towards the marquee, and overheard one of them saying about wanting to stab someone that night.

She said it was “something along the lines of ‘I’m going to stab someone tonight'”, but could not specifically recall the line.

Asked about who said it, she did not know which boy, adding: “It wasn’t like any of the farmers I knew who were there, the voice was more laddish.”

The prosecution had said Charlie was still conscious when police arrived at 12.30am and was able to tell them his name, address and date of birth.

He suffered a cardiac arrest on the way to hospital, with internal bleeding caused by a cut to his aorta, the main artery from the heart.

The teenager, from Milford, Surrey, died on July 25.

The defendant, who cannot be named for legal reasons due to his age, denies murdering Charlie and having a bladed article or point.

The trial continues.