Can't find any Supreme Court cases except with regard to protected speech; but here's a nice summary of the issue I found online:
Prayer as Attempted Murder?
A reader asks an interesting question:
Some Christian Reconstructionists are urging their fellows to pray for the death of John McCain so that Sarah Palin will be become President. [Example here.] Are those who pray for McCain's death guilty of attempted murder, and are those urging them to do so guilty of incitement? It seems to me that they are. Although I don't believe that their prayers can have any effect, it seems to me that this falls into the same category as the oft-discussed firing of an unloaded gun or firing a gun into a bed that turns out to be empty. The intent to kill is present and an action has been taken in furtherance of that goal. Christians should presumably be all the more clear that this is attempted murder insofar as they believe prayer to be efficacious.
This, it seems to me, is a good illustration of the limits of analogy. It's true that asking someone to commit murder may well constitute attempted murder (as well as the crime of solicitation). The test for attempt is generally not just that "an action has been taken in furtherance of that goal" — different jurisdictions require different amounts of conduct, but all require more than just "an action" for an attempt prosecution (as opposed to for a conspiracy prosecution, where an agreement plus an overt act, even a relatively minor one, generally suffices). But when a person has asked another human being to commit the crime, especially when he hopes that the other person will commit the act with no further help from the requester, that would usually qualify. And indeed it generally doesn't matter if it turns out that the request couldn't possibly work, for instance because the person asked would never commit the crime, or was accidentally given an unloaded gun, or some such.
But people aren't the same as God, either to atheists or to religious people. One way of seeing that is that God's action wouldn't be illegal. To those who believe in God, as he is conceptualized by most Americans, God's action wouldn't even be immoral. (It's true that some people say "If God killed people for this-and-such, he would be evil," but usually they are people who don't believe that God does that.) It would be within his authority as, in a sense, the ultimate sovereign of the world.
In fact, if there is an analogy here, it would probably be to a petition to the President asking him to order an assassination that he could lawfully order (or, as to the other part of the reader's question, to exhortations to the public aimed at getting people to petition the President to order such an assassination). I would say that it's even legal to petition the President to order assassinations that are illegal; but, as I said, there's nothing illegal in God's hastening someone's death.
We could try to come up with precise constitutional foundations for this, for instance that the request to the President is protected by the Petition Clause of the First Amendment, and that a request to God is protected by the Free Exercise Clause. Or we could focus on a legal distinction between asking someone to do something that is legal for him (or Him) to do from asking a contract killer to do something that is illegal for him to do. Or we could focus more practically on the relative unlikelihood that a person who tries to cause death by prayer will switch to a gun if prayer fails. (That's one reason we punish attempted killers even when their attempts were factually impossible, for instance because the gun is unloaded: We figure they are quite likely to try with a loaded gun next time.) But we don't have to choose, because all these factors strongly point in the same direction, and strongly suggest that asking God to end a person's life is very far from asking an acquaintance or a prospective contract killer to do the same.
(I should note that there has been a little judicial commentary on attempts to kill by voodoo or withchraft, as best I can tell unanimously opposing criminal liability in such situations. See Commonwealth v. Johnson, 167 A. 344 (Pa. 1933) (Maxey, J., dissenting); Attorney General v. Sillem, 159 Eng. Rep. 178 (1863). But I'm not sure this is a perfect analogy, either, and in any event there's not much real law on that.)
source
