Animals, particularly small rodents are great at smelling and finding entry points into cool or warm houses, crawl spaces, attics, and vehicles. This is why we warn against using poison. Poison works, it kills small animal, and they often die in inconvenient places, i.e your walls, or other hard or impossible to reach places in your home or office. Sometimes they die in your neighbors yard, or your yard and get eaten by a pet, which from time to time causes a pet to die from ingesting a poison filled rodent. We often remove bloated raccoons and opossums from attics that have been feasting on poisoned rats, which can be rare as a homeowner, but something to consider.
You will never eliminate the dead animal smell without removing the dead animal, so if the animal dies 14ft up in your wall next to an ac vent your probably going to smell that animal, (or animals if you use poison) after the animal is removed the smell should start to disapate and after you sanitize the area even more so.
Get Rid Of the Carcass Get Rid Of The Smell ! What you do with the body will depend on the local bylaws in your municipality, but your options include burying, burning, and throwing the body in the trash. Don’t touch the animal directly: either wear gloves or use a shovel to move the carcass around.
To dispose of the body in the garbage back, remove the insulation or debris that surrounds the carcass, then double bag it before placing it in the trash. Remember to seal your outdoor trashcans because other scavenging animals will get in them to retrieve the dead body for food.
You may also be able to call an Dead Animal Removal Service to pick up the body if that sort of thing freaks you out.
Clean the area. With gloves on, use a rag or paper towels to pick up any leftover fur, juices, or anything else left behind by the animal. Spray the area with an enzymatic cleaner, which will break down the organic materials and help eliminate odors.
If you can't locate the animal, buckle up. If the animal died in a very hard to reach place—such as inside a wall—or you may decide to not destroy the finish of your dry wall- whatever the reason is that makes you unable to remove the carcass to get rid of the odor, keep in mind the time it takes for decomposition and the smell to dissipate will depend on the size of the animal, the temperature, and the humidity. Be aware that leaving an animal to decompose could take several weeks or even months.
Use a strong odor eliminator or disinfectant in the area. You can do this by spraying a product like Bac-Azap, hanging Odor Neutralizing Bags, or using a Neutralizing gel.
Replace the bags as necessary and continue using the other neutralizers until the decomposition has finished.
Ventilate the area. Whether you’ve removed the source of the smell or you're waiting it out, ventilation is key to freshening the air and helping eliminate bad odors.
Open as many windows as possible
Get the air moving
Set up a few fans to blow air from inside the house to outside.
https://www.dallasrodent.com/articles/2016/9/9/rats-in-attic