Praying for peace without borders

Tomorrow is the 6th anniversary of a very crappy day in the history of this country. Everyone knows about it. Why? Is it the only catastrophe that has ever happened in this country, or is it because we can point a finger outside our borders. To not discount that event, and with all respect and condolences to the families who lost loved ones in that tragedy, I wonder if any of you can answer the following question.

On April 19, 1995 there was a horrific crime perpetrated in this country. Without the help of the internet, name that event?