Despite warnings that rioting might ensue, 1968 presidential candidate Robert F. Kennedy announced that, "Martin Luther King was shot and killed tonight," to a shocked crowd in Indianapolis, Indiana. The brief speech, made only 2 months before his own assassination, was credited for for preventing violence from breaking out in that city.
Perhaps his message is timely in the wake of the Giffords shooting in Arizona:
"You can be filled with bitterness and hatred and a desire for revenge... or we can make an effort, as Martin Luther King did, to understand and to comprehend and replace that violence... with an effort to understand compassion and love."