A gifted Bristol student who was brutally beaten after breaking up a street row last month has died of his injuries, police have said.
Joseph Dymond-Williams, 17, tried to stop an argument between a woman and her boyfriend on 22 June, but was punched then kicked in the head by two other men.
The prize-winning mathematician, of Whitchurch, suffered three skull fractures and had been in hospital in an induced coma, with his family at his bedside.
An Avon and Somerset Police spokesman confirmed the teenager had died and a murder investigation was under way. A post mortem is due to be held.
Appealing for witnesses, the spokesman said: "It is possible that potential witnesses saw the altercation between a man and a woman and the victim intervening to try to help and then himself being assaulted.
"However, it is thought that they might not have realised the seriousness of the assault at the time."
Joseph was out in Bristol city centre when the argument erupted outside the Que-C bar in King Street just after midnight.
Police said at the time that Joseph, a keen sportsman, was only trying to calm down the situation and was not being aggressive.
A spokesman said: "It was originally a domestic between a man and his girlfriend. The victim intervened to break it up.
"Two other men who knew the woman then confronted the victim. One of the men punched him in the face, causing him to fall to the floor and the other suspect then kicked him in the head while he was on the floor."