A man who lay dead for "some time" before his remains were found in a flat was murdered, police believe.
The victim, who not been identified, was discovered in Woodlands Court, Kettering, at about 18:30 GMT on Wednesday.
Northamptonshire Police believe he was killed "at some point in the last few months".
The force asked anyone who saw suspicious activity at the flat to contact them.
Det Insp Andy McWatt said officers trying to establish when the man was last seen alive.
He said police wanted to speak to "anyone who may have information about those people living in or visiting flat five, Woodlands Court in recent months".