was it ever established who was really responsible for the attempt on hitlers life?
Not definitively, according to Shirer. A German Communist named Georg Elser confessed to the bombing and claimed to been coached by the Gestapo to implicate Best and Stevens in a plot. Shirer thinks his story had holes in it. Whatever happened it looks to me like Hitler was in on the explosion.
"Johann Georg Elser (4 January 1903 - 9 April 1945) was a German opponent of Nazism. He is remembered for his unsuccessful attempt to assassinate Adolf Hitler in 1939."
It is said that, all told, there were 42 attempts made to assassinate Hitler.
This link lists some of the more notable.