A youth has been warned he faces a substantial prison sentence after being convicted of the "cold blooded" murder of another teenager at a party advertised on Facebook.
Jay Whiston, 17, from Clacton, was stabbed at the party in Marlow Way, Colchester, on the night of September 8, 2012, and died in hospital shortly afterwards.
Edward Redman, 18, of Halstead Road, Colchester, had denied murder but was today found guilty by a jury of seven men and five women after four hours of deliberations at Chelmsford Crown Court.
The family of Mr Whiston cheered in court and somebody shouted "scum" from the public gallery as the verdict was returned.
The court heard that the stabbing came after Redman demanded Mr Whiston's friend hand over his drink.
The "unprovoked" stabbing was described by prosecutor Mark Milliken-Smith QC as a "desperate example of the catastrophe and heartbreak" brought about by the use of knives.
Judge Charles Gratwicke said: "You have been found guilty of a vicious, cold blooded stabbing. You'll have to prepare yourself for a substantial prison sentence."
He will be sentenced at a later date when a probation report has been prepared.
Redman did not give evidence during the 13-week trial.
During the trial, Mr Milliken-Smith said the party where the stabbing took place was "advertised to friends via Facebook and by personal word of mouth" by the host.
The court heard that "numbers grew", and some people, whose presence may not necessarily have been wanted at the party, were in attendance.
Mr Milliken-Smith said Mr Whiston arrived at about 8.30pm with a friend.
Around 100 others were at the party, he added.
The jury heard that Redman and his group brought "an air of unease and tension", and that they were "spreading an air of fear".
Redman had demanded that Mr Whiston's friend give him his drink before pushing him.
Despite Mr Whiston, of Aster Close, Clacton, telling him "we don't want trouble", Redman punched and then stabbed him, the court heard.
As his victim staggered away, Redman followed him before hitting him on the head with a bottle and stabbing him again.
After the killing Redman was heard saying on his phone "Just tell them there was a big fight. You don't know anything about it" as he encouraged others to cover up what had happened.
Redman's father Gary Redman, 51, and brother John Redman, 19, were both found guilty of perverting the course of justice.
Shannon Fenlon, 19, from Jameson Road, Clacton, looked shocked as she was convicted of the same offence.
All were remanded in custody ahead of sentencing at a later date.