Tonight my chevrusa and I learned the sugya in Bava Kamma 47b of one who puts poison in front of his friend's animal. A brief synopsis and application of the sugya is at http://businesshalacha.com/en/newsletter/infected:
“A person put some poisoned food in front of his neighbor’s animal,” Rabbi Dayan said. “The animal ate the food and died. The owner sued the neighbor for killing his animal. What do you say about this case?”
“I would say he’s liable,” said Mr. Wolf. “He poisoned the animal.”
“I’m not so sure,” objected Mr. Mann. “The neighbor didn’t actually kill the animal. Although he put out the poison, the animal chose to eat the food.”
“Animals don’t exactly have choice,” reasoned Mr. Wolf. “If they see food, they eat! Anyway, even if the neighbor didn’t directly kill the animal, he certainly brought about the animal’s death.”
“But is that enough to hold him liable?” argued Mr. Mann. He turned to Rabbi Dayan.“The Gemara (B.K. 47b; 56a) teaches that placing poison before an animal is considered grama,” answered Rabbi Dayan. “The animal did not have to eat the poisoned food. Therefore, the neighbor is not legally liable in beis din, but he is responsible b’dinei Shamayim. This means that he has a strong moral liability to pay, albeit not enforceable in beis din (Shach 386:23; 32:2).”
It struck us that it follows that if one poisons another human being by, say, placing cyanide in his tea, which the victim then drinks and dies, the poisoner is exempt from capitol punishment. It would seem that such a manner of murder falls into the category of the Rambam's ruling in Hilchos Rotze'ach u'Shemiras Nefesh 3:10:
Different rules apply, however, in the following instances: A person binds a colleague and leaves him to starve to death; he binds him and leaves him in a place that will ultimately cause him to be subjected to cold or heat, and these influences indeed come and kill the victim; he covers him with a barrel; he uncovers the roof of the building where he was staying; or he causes a snake to bite him. Needless to say, a distinction is made if a colleague dispatches a dog or a snake at a colleague. In all the above instances, the person is not executed. He is, nevertheless, considered to be a murderer, and "the One who seeks vengeance for bloodshed" will seek vengeance for the blood he shed.
(translation from http://www.chabad.org/library/article_cdo/aid/1088919/jewish/Rotzeach-uShmirat-Nefesh-Chapter-Three.htm)
Perhaps this was a davar pashut to everyone else, but for me, tonight, it was a mind-boggling revelation!