A man was tied up and repeatedly stabbed during a robbery in Derby.
The victim was walking his dog towards his home in Wilkins Drive, Allenton, when three men approached him at about midnight on Thursday.
He was taken to his house, where he was tied up before being attacked by the men, who then fled. The man was taken to hospital for surgery.
Det Ch Insp Debbie Edmonds said: "It was an extremely vicious and unprovoked attack on this gentleman."
She added: "There is a suggestion that it was potentially a robbery that had gone wrong but the level of violence that was used was far beyond any that we have seen before.
"Obviously we are quite concerned and desperate to find who was responsible for this offence."
Two of the three attackers are said to be black, the other is believed to be of mixed race and all three wore dark hoodie tops.