The music next door

Premise

A serial killer

One day you went to your neighbors door because you heard loud music coming from their house so you walked next-door and you asked him if he could turn down the music, he apologized and said yes, but while you were standing at the door, you smelt a rotting stench it wasn’t strong, but it was like a faint smell, but you ignored it, assuming it was probably old food or trash.