Quotes from:

From: http://hypertextbook.com/eworld/einstein.shtml#first which also has the content of the first letter to Rosevelt.
• The letter that launched the arms race. A warning to President Roosevelt of the possibility of constructing "extremely powerful bombs of a new type" with hints that the German government might be doing just that. Addressed and dated Peconic, Long Island, August 2nd 1939, it was most likely written by Leo Szilard, the scientist who invented the chain reaction. Nevertheless, Einstein took full responsibility for its consequences, calling it "the greatest mistake" of his life. I have tried to reproduce the formatting as it appeared in the original. This is the only letter for which I have done this.

The following are from: http://en.wikiquote.org/wiki/Albert_Einstein
• I could burn my fingers that I wrote that first letter to Roosevelt. Comment after the bombing of Hiroshima, regarding his letter to Roosevelt warning of the possibility of the development of a nuclear weapon.
• I came to America because of the great, great freedom which I heard existed in this country. I made a mistake in selecting America as a land of freedom, a mistake I cannot repair in the balance of my lifetime. (December 1947?)
• I do not know with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.

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