I suggest looking into Black vs Virginia and Brandenburg v. Ohio
<<<395 U.S. 444 (1969), argued 27 Feb. 1969, decided 9 June 1969 by unanimous vote; per curiam decision. Brandenburg v. Ohio was decided in the context of the significant expansion of First Amendment freedoms in the 1960s. It was the final step in the Supreme Court's tortuous fifty‐year development of a constitutional test for speech that advocates illegal action.
Clarence Brandenburg was convicted of violating an Ohio criminal syndicalism statute for advocating racial strife during a televised Ku Klux Klan rally. The statute was identical to one previously upheld by the Supreme Court in Whitney v. California (1927). The Court fashioned a test that was significantly more protective of dangerous speech than the previous “clear and present danger” test employed in previous cases. Whitney was overturned.
In its various incarnations, the old clear and present danger test had permitted the punishment of speech if it had a “tendency” to encourage or cause lawlessness (Schenck v. U.S., 1919), or if the speech was part of a broader dangerous political movement, like the Communist party (Dennis v. U.S., 1951). (See Communism and Cold War.) The Brandenburg test, however, allowed government to punish the advocacy of illegal action only if “such advocacy is directed to inciting or producing imminent lawless action and is likely to incite or produce such action” (p. 447). >>>
Brandenburg v. Ohio: Information from Answers.com
Being that the acts happened days after the burning of a quran, and that others have burned qurans without similar incident, I doubt anyone would be able to argue "imminent Lawless action" is the result of burning a quran