The family of a teenager fatally stabbed at an end-of-term party at a farmhouse sobbed as graphic mobile phone footage was shown in court.

Charlie Cosser was only 17 when he was stabbed in a fight on the dance floor at the grounds of the farmhouse in Warnham, near Horsham, last summer.

Video dated as taken at 11.59pm on July 22 last year showed the moment he was stabbed three times in the chest, a jury heard.

The Argus: Charlie Cosser died in hospital on July 25 last yearCharlie Cosser died in hospital on July 25 last year (Image: Martin Cosser)

His family comforted each other as they tried to stay calm during the opening of a murder trial at Lewes Crown Court sitting in Brighton today.

Alan Gardner KC, prosecuting, said the mobile phone video caught the moment Charlie, known as Cheeks, was fatally wounded.

The defendant, who cannot be named for legal reasons, tried not to look as the footage was played to the jury several times.

Frame by frame forensic analysis of the video has been carried out by police, Mr Gardner said.

"The knife came into contact with Charlie more than once, three times we say, but it was the stab wound to the central area of his chest which proved to be the fatal injury," Mr Gardner said.

He told the court the defendant or one of his friends took the knife to the party.

The court heard one partygoer said the defendant called out "get the shank" moments before Charlie was fatally wounded.

Mr Gardner said another witness later heard the defendant say "I've stabbed someone" six or seven times.

The defendant sat in the dock in front of the Cosser family.

Wearing a blue shirt and glasses, the 17-year-old from Chessington, Surrey, spoke only to confirm his name.

He was16 when he went to the party last summer.

The defendant's mother was allowed to sit in a box on her own near the dock where she could see her son and he could see her.

She shook her head as the jury was told her son or one of his friends had taken the knife to the party.

The jury heard there were at least 100 people at the party and young people had crowded under a marquee in the garden as summer rain lashed down.

Trouble started when a girl complained about the defendant and said he had tried to touch her up, Mr Gardner said.

Two fights started after Charlie and his friend approached the defendant and asked him to leave.

"Two separate fights erupted on the dance floor," Mr Gardner said.

"It is on that brief altercation on the dance floor the prosecution say the defendant used the knife he was carrying to stab Charlie Cosser in the chest.

"In the darkness and noise of a crowded dance floor his use of the knife and the knife blows went unnoticed.”

The court heard how Charlie was able to leave the tent before collapsing on the grass.

Charlie's father clutched his head and wiped tears from his eyes as the jury heard details of his last moments of consciousness.

Mr Gardner told the court: "At around midnight another party guest was stood on the DJ’s stage when he noticed a boy he knew to be Charlie Cosser lying on the grass.

"It looked like he was in discomfort. He was holding his arms across his body as if he had stomach ache and was wriggling around.”

The court heard the defendant had blood on his hands and clothes.

The teenager gave a no comment interview and the court heard the knife used to stab Charlie has never been found.

Charlie, from Milford in Surrey, died in hospital on Tuesday, July 25, last year.

In a statement from his family, dad Martin, mum Tara, older brother Adam and younger sister Eloise paid tribute to him.

The Argus: The scene in Warnham, near Horsham, last summerThe scene in Warnham, near Horsham, last summer (Image: Supplied)

They said: “Our lives have been destroyed by the tragic and unnecessary loss of our son.

"Despite courageously battling right till the very end of his young and innocent life, his injuries were too severe and he tragically passed away on the evening of Tuesday, July 25.

“He was the most caring, cheeky, loving son and brother we could have ever wished for, and we cannot imagine a life without him.

“Charlie’s wider family are deeply shocked and saddened by the sudden loss.

“Tributes have been pouring in from Charlie’s wide circle of friends which we would like to acknowledge have brought us huge comfort in our darkest hours.

“We would also like to thank on our and Charlie’s behalf, all of the efforts of the emergency services who treated him on the scene, as well as the whole of the critical care team at the Royal Sussex County Hospital in Brighton, who did absolutely everything they could to save our precious boy, with the utmost compassion, empathy, sympathy and care.

“His ridiculously silly sense of humour will be deeply missed by everyone that knew and loved him.”

The defendant denies murder. The trial continues.