Originally Posted by anhailla

there is no drug that renders you unable to move that wouldn't also cause you to stop breathing. Those drugs are paralytics but they would show in an autopsy. Plus you would have to inject the drug into a vein...that would show as well.
The only way possible would be some type of inhalant..but I can't think of one drug that wouldn't be detectable in a post mortem.

a skeletal relaxant is not strong enough, that I can assure you.