Something's Dead Smell?

[Hugh Carnaha]

Howdy guys!

I'm looking at buying a multi-family with an upper and lower. But it has a awful smell of something died somewhere in the upstairs. It seems that it could be in the walls or in the attic, there's also rat poop and possibly cat/racoon poop? Though there are no visible entries. 

I know the whole, "Smells like money!" thing is basically, "change the carpet and carpet pad and it'll 90% of the time get rid of the smell. In this case I'm not so sure it would. 

Does anyone have experience with this before? Any suggestions? Would anyone pass on this because of the smell?

Cheers!