The police and prosecutorial misconduct in Troy Davis' case should have been investigated by the FBI long before the US Supreme Court decided that Davis' almost certain innocence didn't matter, resulting in his execution.
As a Consitutional scholar, President Obama is aware that the Justices' opinions in Brady v Maryland, Imbler v Pachtman, Van de Kamp v Goldstein, Connick v Thompson, etc., all protect the reputations of public servants ahead of the rights of the accused to a fair trial.
It is the FBI's responsibility to investigate public corruption that affects trial outcomes ... Congress and the President need clear and convincing evidence of reason to override Supreme Court rulings.
FBI Director Mueller should address this responsibility or resign, with no other option offered.