For what it’s worth, I suspect that part of the reason Mumia Abu Jamal personally got so much attention has to do with simple organizational dynamics.
Mumia was a Black Panther and then a well-known activist and radical journalist in Philadelphia. He was a member of a number of groups, and in contact with a number of other groups, which (out of necessity) already had well-developed mutual aid and support networks for imprisoned members. That gave him a number of pre-existing and pre-organized advocates, and, not coincidentally, he also got a good lawyer (Leonard Weinglass) with a history of making hay out of politically-charged court cases. All that, combined with his own gifts as a writer and a speaker, and his ongoing stream of writing and speaking from death row, kept his case on the radar long enough for it to be picked up and talked up at length by high-profile supporters like Rage Against the Machine. (Mumia’s history as a Black Panther also helped him out a lot here, since the anarchist revival in the late 1990s brought a lot of sympathetic attention to the Panthers and other radical New Left groups.)
As far as I know, Cory Maye had no real pre-existing support network other than his family, until Balko started writing about the case. Given the situation, frankly, the amount that Radley Balko has been able to accomplish single-handedly on this case, without any significant pre-existing network behind Cory Maye, is inspiring and nothing short of heroic.
This may not entirely explain why Mumia in particular got so much more attention than even other Leftist “political prisoners” in similar circumstances (e.g. Jamil Al-Amin, or Leonard Peltier). I expect that part of it is just that these cases come and go in popularity, and Mumia’s came in at a time when the radical and anarchist Left had (for other reasons) was making a momentary and unusual flash appearance in pop culture. Before Mumia’s case was The Big Thing, Leonard Peltier’s case had been The Big Thing, but the people supporting him didn’t have much media presence. After Mumia’s case was The Big Thing, other cases became The Big Thing in leftist activist circles, but by then the post-9/11 regimentation of popular culture was going on, and things in the media were settling back down to the old permanent war-footing pattern, which required erasing the radical Left.
As far as the “murkiness” of the case goes, personally, I’ve never made any serious attempt to find out whether or not Mumia Abu Jamal shot that cop. Reason being that I don’t care. I’m not Mumia’s priest and I’m not his lawyer either, so my only concerns in this case are (1) that the State shouldn’t murder him in retaliation, no matter what he may or may not have done; and (2) that if he did shoot a cop in an attempt to defend his brother from getting arrested, he was probably justified in doing so. Of course, that’s an argument that you can’t make in court these days, so understandably, but unfortunately, most of the people lined up behind him exhaust a lot of time and energy on arguments that are really, morally and politically speaking, irrelevant.