The body is thought to have been in the Housing New Zealand flat in Titahi Bay for several weeks before being found.
Detective Senior Sergeant Grant Ferguson said the man's body was being examined by a pathologist.
"We're relying on the pathologist to complete her examination and ongoing tests. At this point in time I can't say when that will be, as we're waiting on toxicology results from the deceased."
Mr Ferguson said the dead man had still not been officially identified.