It is not that simple. Witnesses die, memories lapse, evidence ages. Retrying a convicted murder 30 years after the murder is a very tough challenge for any prosecutor, and very easy for a defense team. Through a misaligned DNA finding, a very effective get out of jail free card, regardless of if the person convicted did or do not commit the murder.
And in no way should innocent people ever be in a penitentiary, not for one minute, not for one second. But, many experts' research suggest that people convicted of heinous crimes such as murder that are released because of DNA misalignment- did in fact commit the crime, but the reasonable doubt protection does in fact allow these convicted people to walk free- but in no way should walking free equate to an innocent conclusion.
I am quite sure if the person who murdered the Jonbenet Ramsey, was convicted, and had done the crime, but was released on a misaligned DNA data- you would not want that convicted murderer as your next-door neighbor.