The system is far from perfect; innocent people are convicted all the time. The unusal elements of this case should give everyone pause.
The system calls for reasonable doubt, not a smidgon of doubt. He’s had more than one chance to prove his innocence and, at all times, the courts upheld his conviction.
Either the death penalty is a just punishment or it is not, when one is convicted of crime.
What are the unusual elements?
If you read the case, he also shot another man in the face earlier in the day...which he doesn’t deny...just that he didn’t shoot the police officer later (even though he was shot with the same caliber gun)...probably because shooting the police officer carried the death penalty.
As for his fellow gangsters recanting their testimony later...that is not very compelling.
* Because the sentence against an evil work is not executed speedily, therefore the heart of the sons of men is fully set in them to do evil. Eccl. 8:11