Darrius Skinderowicz, 41, was taken to hospital with serious head injuries late on Monday night after he was found ‘unresponsive’ in the street.
Subsequent enquiries revealed he had been the victim of an assault earlier that evening.
West Yorkshire Police today appealed for witnesses to that incident as they revealed Mr Skinderowicz had died.
The Polish national, who had been living in Castleford, passed away at Pinderfields Hospital in Wakefield on Thursday afternoon.
It is believed he was assaulted by a male attacker at about 6.25pm on Monday at the junction of Carlton Street and Albion Street in Castleford.
Detective Chief Inspector Chris Gibson, of the Homicide and Major Enquiry Team, said: “Following enquiries we are treating Mr Skinderowciz’s death as a murder and are appealing for witnesses to the assault we believe he suffered.
“The junction of Carlton Street and Albion Street would have been very busy at about 6.25pm and at least two buses and several cars would have driven past the location around the time of the offence.
“We would like to appeal for witnesses who may have been in the vicinity, a passenger on a bus who saw what happened or anyone driving past who saw the assault to come forward with any information.”
A 15-year-old boy, who was arrested on suspicion of assault and later murder, has been released on police bail.
Contact the Homicide and Major Enquiry Team on 101, referencing police log 0078 of January 16.
Information can also be given anonymously to the independent charity Crimestoppers on 0800 555 111.