Detectives in Chester want to know how a man from Flintshire came to be seriously injured in the city.
The 23-year-old from Broughton was found unconscious with wounds to his head on Thursday evening after collapsing on Chester city walls.
He was taken to the Countess of Chester Hospital, where his condition is said to be serious but stable.
Cheshire Police say three people have been arrested on suspicion of assault.
Police initially thought the Broughton man had collapsed from drinking, but a scan has since revealed serious head injuries.
Paramedics responded to an emergency call at 2000 BST on Thursday, 3 June, after the victim was found near King Charles Tower, near Kaleyards and Frodsham Street.
A 20-year-old man and two teenagers aged 17 and 16 were arrested on Tuesday and are being interviewed.
A spokeswoman for Cheshire Police said: "The 23-year-old man remains in a critical condition in hospital.
"Multiple lines of inquiry have now been explored by police, including the examination of CCTV, and several witnesses have been traced and spoken to."
Detectives are keen to speak to anyone who may have been in the area of King Charles Tower and the city walls on Thursday evening who may have information about the attack.
Anyone with information can contact Chester CID on 0845 458 0000.