I can imagine the corpse oil dripping to the downstairs..

My hypothesis..

Victim identity still unknown
Contractor‘s testimony unknown

Killer: the 2 foreigners - Friends with benefits doesn't end well, possibly money involved (2020 MCO time), all 3 argued and accidentally killed the female victim.
Questionable: How does the contractor not seen the corpse in the bathroom?

Killer: House owner - Commotion and shit happens, finding a place to hide the corpse (Wouldn't want his family & friends to know), decided to hide the corpse into one of the rental house where the tenants not around.
That's why foreginers will call up owners saying the bathroom have mouse rotten smell.
Questionable: Contractor and owner knows each other. They chose to keep it as secret?
And owner said someone told him that his house got corpse, who the hell knows this? Maybe he made it up.