I just googled it and found this:

http://eji.org/anthony-ray-hinton-exonerated-from-alabama-de...

which has a lot more detail on the specifics of the case (and indeed it is very troubling but great he has been released). Sounds pretty much as theguardian said though.

Disclaimer: I work at the Guardian (not as a journalist though).

Edit: also on WashPo and NYT:

https://www.washingtonpost.com/news/morning-mix/wp/2015/04/0...

http://www.nytimes.com/2015/04/04/us/anthony-ray-hinton-alab...