A fifth teenager has been arrested after an A-level student was stabbed to death outside a house party in Colchester.
Essex Police said the 17-year-old was being questioned on suspicion of assault after being arrested yesterday.
Jay Whiston, 17, died on Saturday night at the event that was attended by about 100 people who had seen details of the party circulated on the internet.
A 17-year-old boy and two 18-year-old men, who were arrested earlier, remain in custody at separate police stations in north Essex. Both are being questioned on suspicion of murder.
Another 17-year-old boy who had been arrested was released without charge, police said.
Jay, from Clacton, Essex, died shortly after being taken to Colchester General Hospital with abdominal injuries.
His mother, Caroline Shearer, said he was protecting a friend when he was stabbed at around 10pm.
"It's every mother's worst nightmare. He was loved by everyone and so caring. My son had never been in trouble with the police before. He hated bullies and hated people being unfair," she said.
Jay, who studied law and business studies at Tendring Technology College, planned to go to university next year.
:: Anyone with information should contact the incident room on 01245 452882