Ann Green

Killed two of her children (attempted to kill the third).
May have been responsible for a series of deaths at the
hospital where she was employed.  

A jury found her not guilty by reason of insanity [PPD] for 
the murder of her first two children and the attempted murder 
of her third, on account of postpartum psychosis (even 
after two weeks' delay in the last case), of which she 
showed no symptoms other than murdering her children. 
The court returned her third child to her. 

http://www.alumni.caltech.edu/~rbell/MadBadAndInnocent.htm

http://www.crimelynx.com/yatesdef.html

http://www.peele.net/lib/excuse.html