The family of a 54-year-old man who was attacked in his Cardiff home say they cannot understand why anyone would want to harm him.
Michael Hewitt has been in a critical condition in hospital since being found at 1130 GMT on Monday, 7 February.
An anonymous caller alerted emergency services and Mr Hewitt was discovered with facial and serious head injuries in Oakfield Street, Roath.
His family have appealed for anyone with information to contact police.
His eldest sister Christine, who has been at his hospital bedside every day, said: "Michael was a very private person and I can't understand why anybody would want to hurt him in this way and cause him such terrible injuries.
"Someone out there knows what this is about and who attacked Michael. I would ask them to contact the police as soon as possible."
Following extensive inquiries South Wales Police established that a man went to his ground-floor flat that morning but left when no one answered.
He is described as white, 5ft 10in, stocky, around 55 years of age with a shaven head wearing dark clothing and a bomber-style jacket.
Det Insp Ceri Hughes added: "We need to know who this man is and who else may have visited Michael over that weekend, particularly from Saturday afternoon.
"I would appeal for the person who made the original 999 call to contact us in confidence.
"This person might have saved Michael's life and will no doubt have crucial information on what has taken place."
Anyone with information can contact Roath CID on 029 20527261 or the independent charity Crimestoppers anonymously on 0800 555 111.