What is it with April?

Offered, without comment:

Assassination of Abraham Lincoln: April 15, 1865
Assassination of Martin Luther King: April 6, 1968

Titanic sinks: April 15, 1912

Branch Davidians at Waco: April 19, 1993
Oklahoma City bombing: April 19, 1995
Columbine high school: April 20, 1999
Virginia Tech: April 16, 2007