If he has a good post-conviction attorney and the facts bear out as you suggest that might be a strong reason to overturn the denial of motion. Anything is possible but, the statistics are not in the inmate's favor as only about 10% of appeals are successful.
https://www.inmateaid.com/ask-the-inmate/my-fiance-asked-for-a-lawyer-during-interrogation-several-times-the-judge-denied-his-motion#answer
Accepted Answer Date Created: November 28,2015