Hypothetically, how would this person know it was RA who he/she saw? And even though LE asked people to come forward who were on the trails that day, this hypothetical person didn’t, instead waited almost six years until he/she suddenly remembers about it after RA is arrested, then informs the defence? Very weak evidence at the 11th hour, I doubt it would help his case at all.
I don’t quite get the point of imagining evidence that might help RA. Is there a source the D has some kind of info or is it simply speculation/rumour which WS TOS doesn’t allow to be discussed.