The Rev. Jesse Jackson on Aug. 14, 2013 (Carolyn Kaster/AP)

The Rev. Jesse Jackson said in a tweet Wednesday that the killing of an Australian baseball player, allegedly by three Oklahoma teenagers who were bored, is "senseless violence" and should be "frowned upon."

Conservatives and others on social media immediately criticized the remark as tepid and insincere — especially in light of Jackson's and other black leaders' strong reactions to the killing of Trayvon Martin, a young black man, by neighborhood watch volunteer George Zimmerman last year.