He doesn't need any documentation my friend. One can judge Hitler and the Nazi's by their actions - they were clearly not Christians.
They claimed to be.
The were certainly not good Christians and not representative of either modern Christianity as a whole or what modern Christians of any subset consider to be correct behavior for a Christian.
I think it would be reasonable to say they forfeited their claim to Christianity by their behavior, but it is not correct to say they did not lay claim to being Christian.