What reason did hitler give for attempting to annihilate the jewish people?

Hitler thought that the economic downfall was the Jews fault.

For the second question

Kristallnacht: November 9-10. That night in Germany, thousands upon thousands of Jews were subject to terror and violence by the Nazis. Over 1,000 Jewish synagogues and over 7,500 Jewish businesses were destroyed, and approximately 30,000 Jewish men were arrested and taken to concentration camps.