The conviction of a teenage girl who used a mobile phone to film a man being kicked and punched to death in a so-called "happy slapping" attack is thought to be the first of its kind in England and Wales, prosecutors said today.

The 15-year-old, who cannot be named for legal reasons, admitted at a hearing yesterday recording part of the violent attack that killed Gavin Waterhouse, 29.

Leeds crown court heard how Waterhouse was attacked by Mark Masters, 19, and a 17-year-old youth, who also cannot be named, in Keighley, West Yorkshire, in September last year.

The victim managed to return to his flat after the assault but died from internal injuries.

Both men admitted manslaughter at a previous hearing. The girl yesterday pleaded guilty to aiding and abetting manslaughter.

According to the crown prosecution service (CPS), the girl was handed a mobile phone by one of the attackers and told to "video this".

She then approached Waterhouse and asked him for money before recording the attack upon him that followed.

Prosecution witnesses said they saw and heard the attackers boasting about what they had just done, saying it was not the first time they had attacked the victim.

They also shared the video footage of the incident with friends after the attack.

Judith Naylor, of CPS West Yorkshire, said: "As far as I am aware, this is the first time a suspect in England and Wales has been successfully prosecuted for aiding and abetting murder or manslaughter, for the filming of an, inaptly called, 'happy slapping' incident.

"We have seen and heard of many instances in recent months and years, where youths have been encouraged by their peers to attack innocent people, without words ever having been used.

"The message is this: if you stand by and watch your friends committing brutal crimes and video-record their acts for your, or for others', amusement your actions will not be ignored by the law enforcement agencies and prosecution may follow."

Yesterday, Judge James Stewart heard how the defendant claimed she did not know Masters before he passed her the phone and asked her to use it.

She even had to ask him how to use the camera before filming about 15 minutes of the violence.

The girl will be sentenced at a date to be fixed along with Masters, of Parkwood Rise, Keighley, and the other youth.