Today in history: On April 4, 1968, civil rights leader Martin Luther King Jr., 39, was shot and killed while standing on a balcony of the Lorraine Motel in Memphis, Tennessee. King’s death triggered a wave of unrest in cities across the United States that killed 43 people and injured more than 3,000. Also on this date: In 1841, President William Henry Harrison succumbed to pneumonia one month after his inauguration, becoming the first U.S. chief executive to die in office; Harrison’s vice