Christa-- Thanks for the detailed off-page email.Shows you have done considerable homework!
Found this information on the Web.The phone number may be a little dated, but is a place to start.The Website looks to be very informative and will likely be a great resource for you.
I include the information from ABMC which has the proper designation of his Squadron and Group.
Robert P. Rietze Staff Sergeant, U.S. Army Air Forces 39827023 75th Bomber Squadron, 42nd Bomber Group, Medium Entered the Service from: Idaho Died: January 17, 1946 Missing in Action or Buried at Sea Tablets of the Missing at Manila American Cemetery Manila, Philippines Awards: Air Medal with 4 Oak Leaf Clusters, Purple Heart
42nd Bomb Gp (M), 69th/70th/75th/100th/390th Sqdns: F.J. Saler (903) 868-1256