Paul Groom, 48, was found with head injuries at his home in Fazakerley, Liverpool and died later in hospital on 10 December.
Detectives are hoping to trace passengers who travelled with him on the 17 bus from Kirkby to Fazakerley two days earlier.
A man is to stand trial accused of his murder in June.
Mr Groom boarded the bus at Valley Road at 06:14 GMT and got off on Lower Lane in Fazakerley, said police.
He was wearing a green camouflage coat and was with his dog, a brown whippet, which he was often seen walking in the Fazakerley area, said police.
Det Insp Cath Haggerty said: "We specifically need to speak with anyone on this bus who may have spoken to Paul or remembers having any kind of interaction with him.
"If you were on this bus or recognise anyone from the images, please contact us immediately."
Detectives said they are also keen to speak with anyone who may have seen or spoken with Paul between 15:00 on 7 December and 10:00 on 10 December.
Mr Groom, originally from Wrexham, died from a blow to the head, a post-mortem examination found.
Michael Hill, 32, of Oakdale Close, Kirkby, is charged with murder and is due to stand trial in June at Liverpool Crown Court.
CCTV images showing a man travelling on a bus days before he died have been released as part of a murder inquiry.