Robert Simpson was found dead in his home in Mayfield Drive, Armadale, at around 9pm on Saturday October 6.
Lothian and Borders Police say the 67-year-old was the victim of an assault and suffered serious head injuries.
Mr Simpson, also known as Ronnie, was described as a small, frail man who often walked with a stick or crutch. His family, which includes his daughter Kay and son Ross, have said they are devastated by the loss.
Crimestoppers are offering the reward for anyone who can help the police with their investigation to trace the killer or killers.