A man with a guitar could hold vital clues about a fight which left a 22-year-old man critically injured.
The victim was beaten up in Castle Square, Brighton, shortly before 5am on Sunday and left fighting for his life.
Police say the suspect is a black man aged between 22 to 26 who was wearing a dark hooded top and jeans at the time.
He ran off through Pavilion Gardens and was seen shortly afterwards getting into a Brighton and Hove green and white taxi heading towards Worthing.
Detectives says they were told about the attack by a man with a guitar. He was wearing a black and grey chequered coat with the hood up and was carrying the instrument in a black guitar case on his back.
Detective Sergeant Julie Greenwood said: "The man with the guitar alerted our officers to the fact that the victim had been hurt and that it appeared serious. This may well have saved the victim's life.
"He may have seen the attack taking place and will hopefully be able to identify the suspect as they were in a newsagents at the same time moments earlier. We need to speak to him."
Investigators are still trying to trace the taxi driver who took the suspect to Durrington or Lower Salvington in Worthing between 5am and 6am after the assualt took place.
Police say the taxi driver had a Middle Eastern appearance.
DS Greenwood said: "I cannot underestimate how important it is that the taxi driver comes forward to speak to us. He holds key information that may be crucial to bringing the offender to justice for this."
Witnesses who saw the attack in Castle Square next to the NatWest bank or what happened afterwards to get in contact.
Anyone with information should email email@example.com quoting Operation Bunker, call 101 or contact the independent charity Crimestoppers anonymously on 0800 555111.