A photo of two people police would like to speak to following the death of a man who had been sleeping outside Leeds Station has been issued.
Terry Bailey, 39, was assaulted in the early hours of 29 August and died in hospital later.
The men are not believed to be directly involved, but could have information about an argument that took place.
They got on a train at Leeds to Manchester Piccadilly, said British Transport Police.
Det Ch Insp Glen Alderson said: "We believe they may have witnessed a verbal altercation that took place before the fatal attack so it's really important we talk to them."
The Leeds West Indian Carnival had been held in the city over the bank holiday weekend and Mr Alderso said the two men in the picture "may have been part of a larger group that went to it".
Daniel Goodall, 56, of Poplar Mount, Bramley, Leeds, and Jamie Loftus, aged 28, of no fixed address, have been charged with manslaughter.
They are to appear at Leeds Crown Court on 28 September.