Neighbours were aware of the strong smell wafting through their corridor at least a week before a body was found in a Housing Board flat in Outram on Tuesday.
Police called to Block 52 Chin Swee Road that night were seen leaving the flat with a metal pot and a bag, according to Chinese-language newspaper Lianhe Wanbao.
The police said on Wednesday that they were investigating the case as one of unnatural death.
When The Straits Times visited the unit yesterday, no one answered the door. A chain with a padlock secured the gate.
A handful of residents living on the same floor told ST that the stench became very strong while the police were questioning them.
Mr Ken Ong, 39, who lives on the same floor, said the smell was of "something rotting" and it was so "unbearable" that he closed his door immediately after the police finished asking their questions.
ST understands that the occupant of the unit was a man in his 20s who moved in about three or four months ago and lived alone.
He was described as tall and of large build by neighbours, with several saying that loud sounds from the TV could often be heard coming from the unit, and the door was often left ajar.
Several residents also said that they last saw the man a week or two ago, although one resident, who did not want to be named, claimed she saw him sweeping outside his flat on Monday morning.
ST understands that a couple with four children had lived in the flat before moving out earlier this year.