It was new evidence that helped free him. Marco's brother Miguel was an accessory to the gas station robbery and was imprisoned for 18 months. It seems after all this time he decided to inform police of the shooter- Antonio Salgado, and recorded a conversation of Antonio admitting guilt.
http://people.com/crime/los-angeles-man-marco-contreras-freed-attempted-murder/
Marco sounds like a great person who has endured much. I hope one day he can break free from another kind of captivity.