1) No physical evidence
2) The weapon of the murder wasn't found
3) 7 of the 9 witnesses recanted their testimonies
Glad we don't hand out execution as a punishment over here, I remember I ignorantly once said I wouldn't mind having over here, but it doesn't bring the murdered back to life, all you're doing is making yourself a murderer. It's not going to bring the police officer that died back, I think the idea that their isn't enough evidence to say he actually committed a crime makes it even worse on this occasion though.
Thoughts?
You can read more on the case here,