The body of a man, who was in his 60s, was discovered in Cedar Close, Southend, on 8 August.
His death had been treated as non-suspicious, but a post-mortem examination on Friday showed he had suffered "serious internal injuries".
The suspect, who is in his 40s, was arrested at his home in Southend.
The victim had been assaulted just eight days previously by three men during a burglary at his home, and detectives are now investigating whether it was linked to his death.
Det Con Insp Martin Pasmore, of Essex Police, has appealed to the public for more information.
"This is a complex investigation and I believe that more than one person was involved," he said.
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