Hello everyone -- first post here from a long time lurker.
When I was ten, our family took a two week vacation. Probably during the first couple of days we were gone, our housesitter died in our home. When we came home, the smell of decomposition was unbelievable. The smell of a decomposing human body is unique and distinctive and like nothing else.
We had to move out of the house for a month while disaster services completed a full restoration, which included carpet and drywall replacement and disinfection with extremely strong, very specific chemicals. Everything in the house had to be cleaned; we lost a lot of our belongings, as the smell of death permeated objects that could not be cleaned or salvaged. To say it was vile is an understatement. It was an extremely traumatic event for our family.
The reason I'm telling this story is that even years later, occasionally we would catch a feint whiff of decomposition. It obviously wasn't as strong or new as when the incident first happened, but it was, like I said, a very distinctive smell. It finally stopped, but it just goes to show that the gases and chemicals that a decomposing body produces is just insane!
If a body were left in a car long enough to decompose to the point of smelling, I personally would have no doubt that the smell could linger in the car long after the body itself was removed. Yes, it's that strong and permeating!