There are several products that are supposed to neutralize odors as
opposed to masking them with perfume.  One that I have used is called
XO and it does work for all kinds of horrible smells including dead
animal smells.  It is diluted with water and sprayed or wiped on the
contaminated surfaces or just sprayed occasionally in the area where
the odor is lingering.  It is especially good at getting rid of the
widely distributed subtle odor that permeates surrounding areas.  If
the source is still there, it will not work as well so be sure to get
rid of as much as you can first.

XO can be gotten from janitorial supplies in large quantities for a
much better price than retail stores.  If you can't find it anywhere,
you can also get it from veterinarian supplies (or from your vet) or
better pet stores.  Vets use it to neutralize the odor of anal sac
fluids.  If it neutralizes that, it will work on anything.

I forget the names of the competing products, but I have used some
of them that work well, too.

Spencer Chase
http://www.SpencersErolls.com/