The Answer is : C.

Choice (C) is the correct answer. The spectator intended that the crime be committed and shouted encouragement. He had the appropriate mens rea; shouting encouragement was the actus reus. Therefore, as a matter of substantive criminal law, the spectator is guilty, as an accomplice, for the murder of the customer. Technically, the spectator is a principal in the second degree because he was present and commanded or otherwise encouraged the principal in the first degree to commit the crime.

Choice (A) is incorrect because the standard discussed relates to First Amendment free speech cases. The spectator is not being prosecuted because he uttered words; he is being prosecuted for his intent to commit a crime which, coupled with the action of uttering words, became a criminal activity. 

Choice (B) is incorrect because oral encouragement does make him an accomplice to the crime; therefore, answer choice (B) misstates substantive law. 

Choice (D) is incorrect because mere presence, even coupled with intent, is not enough to make someone guilty of committing a crime.