Brendan Harris attacked Sophie Lancaster, 20, as she begged him and four other youths to stop beating her boyfriend, art student Robert Maltby.
Preston Crown Court heard the assault was totally unprovoked and the two victims from Bacup, Lancashire, were singled out because they looked different to their attackers.
Miss Lancaster, a gap year student, died from serious head injuries two weeks after the attack in Stubbylee Park, Bacup, in the early hours of August 11 last year, while Mr Maltby, also a Goth, survived.
A jury of nine men and three women found Harris guilty of murder within hours of retiring.
After the verdict trial judge Anthony Russell QC lifted an order banning identification of Harris and Ryan Herbert, 16, who had pleaded guilty to Miss Lancaster's murder.
Harris had denied the murder charge but pleaded guilty to causing grievous bodily harm to Mr Maltby after drinking two litres of cider, a bottle of Stella Artois lager and "quite a lot of" peach schnapps.
Herbert admitted murdering Miss Lancaster before he was also due to go on trial. He also pleaded guilty to assaulting her boyfriend.
Three other males, two aged 17 and one 16, who can still not be named, also pleaded guilty to assaulting Mr Maltby.
The young couple, who had been going out for six months, were walking home from a friend's house to their flat in King Street shortly before midnight when they began chatting with a group of teenagers.
They drifted into the park where the good-natured conversation continued and they even handed out cigarettes to the group.
However, the mood changed suddenly when the five teenage boys savagely turned on Mr Maltby in the skate park area.
Someone was heard to shout "let's bang him" and the Harris started the orgy of violence with a flying kick to his head.
The gang, described in court as "acting like a pack of wild animals", then punched, jumped and stamped on his head until he was unconscious.
Miss Lancaster cried for them to stop as she cradled her boyfriend's head on her lap.
Her plea went unheeded as Herbert delivered a volley kick to her face, with Harris joining in to kick and stamp on her head as she lay on the ground.
When paramedics arrived and found the couple lying side by side covered in blood, they could not tell what sex she was such was the severity of the injuries to her face. The pattern of some footwear was still on her head.
Both fell into comas but Miss Lancaster never regained consciousness and died in hospital 13 days later.
Mr Maltby spent two weeks in hospital, suffered memory loss and has no recollection of the attack, the court heard.
Harris told the jury he started the chain of events when he punched Mr Maltby.
He told police he did not know why he did it and was just "drunk and showing off".
Giving evidence, he said he stood aside as up to four youths waded into Mr Maltby and then watched the attack on Miss Lancaster by Herbert.
However, a number of witnesses, all aged between 14 and 17, some who knew Harris, said though he was "in the thick of it" as he joined in the kicking and stamping.
Harris argued that Herbert was solely responsible and the witnesses to the incident in the badly lit park must have been mistaken.
The jury was also told no traces of blood from Miss Lancaster were found on Harris's shoes or the clothing he wore on the night of the attack.
Harris, dressed in a dark grey suit, black shirt and not wearing a tie, did not react in the dock as the unanimous verdict was read out.
Family members and friends of Miss Lancaster who were sitting in the packed public gallery gasped and began crying as the jury foreman answered "guilty".
Judge Russell praised the families of both Miss Lancaster and Mr Maltby, saying they had acted with dignity during what must have been "a very, very harrowing ordeal".
He also publicly thanked four witnesses who had helped the victims and given evidence in court despite loyalties that he described as "very strained". He ordered them to be awarded £250 each by way of thanks.
The police and the Crown Prosecution Service were also thanked before the judge turned his attention to the jury.
He said they had performed probably the most important public duty possible during "a most harrowing case" and gave gratitude for their service.
The judge also explained that he was duty bound to give Harris and Herbert life sentences given their convictions for murder, but that he would set the tariffs after reading pre-sentence reports.
Sentencing was set for April 28.
Outside court, Sophie's mother, Sylvia, 52, said: "I stand outside this house of justice today, not as Sophie's mother, but as her voice. Her voice that was cruelly silenced in a single mindless act.
"Sophie was a thoughtful, sensitive individual and she would not have wanted her death to have been in vain.
"I hope therefore that, as a society, we can use what has happened to reflect on where we are going and what changes we need to make to prevent others suffering in this way.
"Finally, I must thank my family, friends, the police and the thousands of strangers from around the world whose support has been such a comfort to me from the start of this ordeal."
It also emerged that Herbert, of Rossendale Crescent, Bacup, and Harris, of Spring Terrace, Bacup, have previous convictions after they chased a youth out of Stubbylee Park and assaulted him.
Both were given six months' community service orders at Rossendale Youth Court for the attack in April last year.
They targeted a 16-year-old boy who was in their group as they kicked and stamped on him.
Outside the courtroom, Miss Lancaster's friends and family hugged each other and the police officers in charge of the case.
Footage was also released that showed Ryan Herbert in a mocked-up music video called "Hands up for Bacup".
In it, the 16-year-old is seen with three other youths performing a rap about the town over footage of various local landmarks.
In one repeated section, all four can be seen menacingly swinging wooden poles as they stride towards the camera.
Herbert, dressed in a black hooded top, is also seen confidently swaggering down a street and crossing a road.
He does not sing on his own but only forms part of the chorus - the "Bacup Crew".
In a section sung by one of the other youths, a boy raps: "Enough men die in this town/You mess with GBH you go down."
The video was put together as part of a youth project and was uploaded on to internet video-sharing sites but has since been taken down.
Detective Superintendent Mick Gradwell, Senior Investigating Officer at Lancashire Police, said it was one of the most violent murders he had come across in his lengthy career.
He said: "It was a totally unnecessary and appalling set of circumstances.
"I do not think Herbert and Harris have recognised how violent the attack was. There was no reason for it.
"They have just done it without thinking but they have seemed to have enjoyed it and carried on remorselessly kicking at two very defenceless people who were unable to protect themselves because of the level of violence inflicted upon them.
"Their behaviour that night was that they were doing what they wanted with their parents doing nothing about it or not knowing about it. There was a total lack of parental control.
"I am very critical of some of the parents involved. I really don't think they have taken completely seriously how repulsive this incident was."
He said that when Harris was initially interviewed about the assaults he was "laughing and joking" with his mother.
"The interviewing officer had to speak to Harris's solicitor to make sure they knew the gravity of the situation because they were laughing and joking.
"The general attitude of the defendants' parents during the whole process has been appalling.
"Sophie's mother also commented to us that the three defendants who were convicted of assaulting Robert Maltby were sniggering at her outside court before the start of the trial."
The three youths, who cannot be named, were initially on bail at the beginning of the trial but were then remanded in custody by Judge Russell.
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