Detectives are questioning four teenagers over the murder of an A-level student who was stabbed to death outside a house party advertised on Facebook.
Jay Whiston, 17, was knifed on Saturday night at the gathering that was attended by about 100 teenagers in an affluent area of Colchester, Essex.
It is believed details of the event were circulated on the social networking site, but that a number of uninvited guests turned up.
Jay, of Clacton, Essex, was taken to Colchester General Hospital with abdominal injuries but died shortly after his arrival, having been stabbed at around 10pm. A provisional post-mortem examination showed he died from a stab wound.
Two 17-year-old boys and two 18-year-old men, all from Colchester, are being questioned at separate police stations in north Essex on suspicion of murder.
Jay, who studied law and business studies at Tendring Technology College, planned to go to university next year. The victim's mother Caroline Shearer, 46, said her son was trying to protect a friend when he was attacked.
"My son had never been in trouble with the police before. He hated bullies and hated people being unfair," she said. "I still feel numb but I'm starting to feel angry now. How can thugs ruin innocent lives at their will? There's no rhyme or reason to it."
Detectives from Essex Police said every teenager at the party in Marlowe Way was a potential key witness.
Speaking on ITV Daybreak, Mrs Shearer wept as she described her son.
"He was kind, loving, honest, an A-level student studying law, he had his whole life mapped out didn't he? He was going to get married, he was going to have two girls. He worked since the age of about 13 every Saturday with his dad," she said. "He has just gone."