On April 19, 1993, the standoff between federal agents and a religious cult known as the Branch Davidians ended in a deadly fire in Waco, Texas. Seventy-six people were killed.
Two years later on April 19, 1995, the Oklahoma City bombing of the Alfred P. Murrah Federal Building killed 168 people.
The Columbine High School shootings took place on April 20, 1999. Twelve students and one teacher were killed. The two students involved then committed suicide.
On April 16, 2007, 32 people were killed at a school shooting at Virginia Tech. It was the deadliest shooting by a single gunman in U.S. history.
On April 20, 2010, 11 people were killed when the Deepwater Horizon oil rig exploded in the Gulf of Mexico. Oil leaked for months until the well was finally capped the following September.
