The pensioner was attacked in his apartment at Affoltern am Albis early last month by a gang of three young men and a 15-year-old boy.
The victim, reportedly from Sri Lanka, died ten days later from his injuries.
Police said the man was initially taken to hospital suffering from broken ribs, a femur fracture and skull-brain trauma.
The suspects, the eldest of whom was 20, have admitted to attacking the man, the local prosecutor reported on Monday.
However, the prosecutor said contradictions remain over what exactly happened.
Several days after the elderly man died, the four suspects were arrested following an investigation by cantonal police in Zurich.
Police have not yet established a motive for the attack.
News of the crime has rocked Affoltern am Albis, a normally placid village with a population of 1,100.
The last time the community hit the news headlines was over a report about a craftsman working there who is reputed to be the last pipe-maker in Switzerland.