You might find the links on my profile useful in your search for truth. May God bless you in your search... Seek and you will find!
One of the deciding factors was that the Reich had already gone to the Church and offered to "trade Jews" for verbal support from the church. Something that Pope Pius XII wept over when the "Jew laws" were being passed in Italy. The fear was that Hitler would offer to "trade Jews" for land, peace, a cease fire, etc., something that the Allies could never accept. They were also afraid that if they bombed the camps that Hitler would either use it as propaganda that the "Allies killed the Jews" or realize that we knew what he was doing and would speed up the executions.
I'm sure the debate over whether or not we could have done more to stop the Holocaust can go on forever but personally I believe that Roosevelt was right, the best way to stop it was to win the war.
It's a great book and it talks about the attacks on the Catholic church by Hitler including all of the monks that were murdered after the Church denounced Nazism.