The short of it: Robert Coney was convicted of a crime he may or may not have committed. The only thing that’s certain (as there are no surviving witnesses, prosecution, or transcripts) is that there were some improprieties in the prosecution that should have set him free a long time ago, as it had previously been so ordered.
Now, this article, as well as others, makes a passing reference to his escaping from prisons in South Carolina, Louisiana, and Mississippi. Since the crime was a grocer store robbery, that does not seem on the surface to fall under a Federal crime, so it wouldn’t seem that should have been moved across state lines for a State crime. The crime apparently occured in TX, where he was eventually freed.
The GQ:
Why was he imprisoned in the other states? Were those simply the states where he was caught after he escaped from TX, or was there some other reason?