Detectives are questioning three 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.
A 17-year-old boy and two 18-year-old men, all from Colchester, are being questioned at separate police stations in north Essex on suspicion of murder.
The victim's mother Caroline Shearer, 46, said her son was trying to protect a friend when he was attacked.
"It's every mother's worst nightmare. He was loved by everyone and so caring," she added.
"My son had never been in trouble with the police before. He hated bullies and hated people being unfair.
"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."
Jay, who studied law and business studies at Tendring Technology College, planned to go to university next year.
Detectives from Essex Police said every teenager at the party in Marlowe Way was a potential key witness.
Senior investigating officer DCI Simon Parkes said: "This really is tragic loss of life that we, but more importantly, this boy's parents have to deal with."
"This murder took place in an affluent area of Colchester and at a house party which had a garden that could cater for the 100 or so teenagers that were present.
"Although we don't yet know the details of what went on, we're slowly piecing together the sequence of events that led to this boy's death.
"We're speaking to those who were at the party, but we're mindful that there may have been others who left either before the stabbing or in the immediate aftermath before we arrived.
"Everyone at this party is a key witness whether they saw anything or not and we would urge them to contact us."
The killing has shocked neighbours in the quiet residential street, which is on the outskirts of Colchester.
A number of homes were sealed off as police searched for clues yesterday. Empty bottles of vodka and cans of lager could be seen strewn across the front gardens of properties in the street.
Marie Partner said a woman and her teenage daughter, who were hosting the party, had spoken to neighbours to apologise in advance for any extra noise.
Ms Partner said: "The mother and daughter took it upon themselves to tell the neighbours there was a party taking place and to apologise in advance if there was slightly more noise than normal.
"It's so sad. The first I knew about it was seeing the police arrive and the area being cordoned off."
Another neighbour described witnessing "scores of young people" outside his home on Saturday night but said it was rare for big gatherings of teenagers in the street.
Floral tributes and cards have been laid at the scene, with messages of condolence also paid on Twitter and Facebook.
One message left near the house where the party was held read: "Words can't explain it Jay but our thoughts are with you. God bless."
Another read: "RIP Jay. You were a great guy, friend and colleague. You will be dearly missed."
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."