Mattie Jane & Thomas are my paternal gg-grandparents. I've never been able to find a death cert for him either, and I agree that he is not the son of James Murray & Sarah Birdwell.
The only other information I can give you that I know is true is that Thomas was married to another woman before Mattie Jane. We think her name was Fanny Chance. I got this information from a descendant of Mary Magdalene "Mollie" Murray. Mollie was the only daughter of Thomas Murray and Fanny Chance. Mollie married Noah C. Harris and died in Marion County in 1934.
Noah Harris was the brother of my maternal g-grandpa, Will Harris. Please let me know if you turn up anything on Thomas Newton Murray.
Donna O'Brien