I am writing a twisted murder mystery about a rich socialite who is also a serial killer. I am trying to find out how she can poison someone without it being detected in a toxicology report. Killers do it all the time on TV, but in real life, I am not sure there is any poison that cannot be detected in an autopsy. Alternatively, she could kill the person another way, but her M.O. is to kill people without the police knowing it was a murder. Any ideas?