Formaldehyde.

[Dynamics]

You ask a good way, but the truth of the matter is that there's only one proper way to do it. The hard way. Gotta remove all the upholstery, loose fabrics and internal carpeting, spray 'em good with an odour neutraliser and then leave 'em out to hang in the backyard or something. Then you have to do the same with the fabrics on the seats in the car. It's a real pain in the ass, but it get's the job done.

An alternative way if you can't be bothered to do the thorough job is to just spray the car over with some kind of odour neutraliser. However, I can't guarantee the smell of death can be neutralised .__.

Unfortunately you live in California and I live in Melbourne, so I don't think I can recommend any of my local brands, as I doubt they'd be available to you.

Hope I've helped.