Thanks. It's good to know that the plot device is plausible. Now: How are the cars cleaned? High-pressure water hoses over a special track with a trough that carries away the water? The bones will be discovered at that point.

I am thinking of a serial killer who knows it may be years before a railroad takes back into service grain hoppers stored on an overgrown siding almost invisible through trees way out in the country. (There is such a place in Upper Michigan on the Escanaba & Lake Superior short line; I believe the E&LS stores excess cars for other railroads.)

The first bones are discovered way out in Nebraska at a UP yard when a cut of stored cars is sent there for cleaning. Naturally the cops discover where the cars were stored, and the local Upper Michigan sheriff who is the hero of my mysteries goes out to the siding and checks the remaining cars . . . and finds human remains in several of them.

Does this also sound plausible?

Are there other kinds of cars where bodies can be hidden? I suppose tank cars, but it doesn't seem to me that bones could be easily flushed from them.