May 4th in history:
Four students died and nine others were wounded at Kent State University in Ohio on May 4th, 1970, after the Ohio National Guard began shooting to break up a demonstration against fighting in Vietnam and Cambodia.
On this date in 1886, a bomb exploded during a labor rally in Chicago. A policeman was killed by the explosion, and other officers fired into the crowd, leading to what became known as the Haymarket Square riot.
And a two-day riot at Alcatraz Prison in California ended on May 4th, 1946. Five people were killed in the uprising.