Do you recall the one that didn't get away?
A cyanide tylenol (or maybe some other pain reliever) was fed you some poor smuck by his wife to collect his insurance. The death was ruled a heart attack and the wife started thinking that she could have gotten double indemnity if it had been a murder.
So, she placed some more of the poison pills in a store and when some poor woman died she called the cops and told them her husband had taken pills from the same store.
Bottom line it drew attention to her and they wound up catching her.