Heber J. Grant records that J. Reuben Clark authored the 1P statement condemning the Nazis in October 1942.
Heber J. Grant, Journal, October 3, 1942, MS 1233, CHL
October 3, 1942—continued
At 10 o'clock attended the first session of the Conference. President Clark read the Message of the First Presidency. It was a very comprehensive, fine address. Brother Clark practically wrote it all. We consulted together about it. I would have been perfectly willing for him to sign his name, but he said, "No, it is the First Presidency's Message, and not his own." We were a unit in approving it.