Detectives have arrested two teenagers on suspicion of murder.
A 15 year-old boy and a 17 year-old male were being held in custody where they were to be questioned by detectives.
Merseyside Police confirmed a man died following an unprovoked attack in St Helens on Friday night.
Len Saunders, 65, from St Helens died on Sunday.
A Home Office post mortem will take place to establish the cause of death.
Detectives are appealing for information.
The 65-year-old victim was walking with his friend along Ward Street just before 7pm when they were approached by two younger men.
One of the men asked Mr Saunders and his friend if they smoked and if he could borrow a cigarette. When the pair said they didn’t smoke, the victim was punched in the head by one of the offenders and fell to the ground.
The two offenders then ran off along Ward Street while Mr Saunders’ friend called the emergency services.
Mr Saunders was taken to hospital with a serious head injury before being transferred to Walton Neurological Centre in Liverpool for treatment.
Detective Inspector Cath Haggerty said: “This was a completely unprovoked assault by two youths on a much older man who was simply out and about with his friend. When they told the offenders that they didn’t smoke so couldn’t offer them a cigarette, the 65-year-old gentleman was punched in the face. We believe the punch has knocked him to the floor where he has hit his head and suffered a really serious injury. I’m sure people living in the area will be disgusted by this incident so I would appeal for them to help us bring the offender or offenders to justice.
“It was a wet evening but plenty of people will still have been out walking or driving past at the time. If you remember seeing two young men acting suspiciously before the attack at 6.50pm or running away afterwards then please call us on 0151 777 6064 or leave information anonymously with Crimestoppers on 0800 555 111.”