Albert Speer was a very smart man, he used Hitler artistic asperation to get close to him and throught him to gain a position of power in the TR, after the war, at the Nuremberg trials he understand that the allies don't want to hear excuses like "I didn't know" or "it's was all Hitler and Himler" so he confess as a way to save his own neck, it's should also be mention that Fritz Zauckel, who worked under Speer was hanged while Speer got only 20 years in jail.
Contrary to his claims, he did know about the atrocities, he was present at the
Posen Conference and was responsible to the expell of Jews from Berlin to concentration camps in Poland.
The only thing that could be said to his favour his that he disobey Hitler order to destroy Germany inferstracture and the he influence Doenitz in his appial to the German to cooperate with the occupetion force.