The Legal Answer:
An officer's job is to turn over all evidence to the State's attorney and testify at trial truthfully. It is the State's attorney's job to turn over all evidence in discovery to the defense; to only prosecute people they believe are guilty or likely guilty; and to remedy clear and convincing false prosecutions as outlined in ABA rule 3.8 which is echoed in many state laws.
Rule 3.8: The prosecutor in a criminal case shall:
(a) refrain from prosecuting a charge that the prosecutor knows is not supported by probable cause;...
...(d) make timely disclosure to the defense of all evidence or information known to the prosecutor that tends to negate the guilt of the accused or mitigates the offense, and, in connection with sentencing, disclose to the defense and to the tribunal all unprivileged mitigating information known to the prosecutor, except when the prosecutor is relieved of this responsibility by a protective order of the tribunal;...
..(h) When a prosecutor knows of clear and convincing evidence establishing that a defendant in the prosecutor’s jurisdiction was convicted of an offense that the defendant did not commit, the prosecutor shall seek to remedy the conviction.
If this new exonerating evidence is turned over to the prosecutor they would be required to submit it to the defense and the trial would likely be postponed for both sides to evaluate the new evidence. If they suppress the evidence it would be grounds for appeal and disbarment of the prosecuting attorney.
It is not the officer's job to direct the trial, just supply evidence that supports the truth. But it also wouldn't help if the State's own witness suddenly started offering testimony contrary to supporting guilt and in light of new evidence the prosecution may reevaluate to not have this happen.
The Ethical Answer:
Kind of sticky going into ethics and the exact right response to this situation, but it sounds like the answer you want.
Assuming an ethical prosecutor the this would be the same as the legal answer. If this is not the case and the officer reasonably believes evidence will be suppressed, they could turn over evidence to both parties directly or to the prosecution and make the defense aware that he submitted evidence. He could also notify the state bar association of the suppression by the prosecution should that happen.
Of course these actions may be at peril to their job as an officer despite whistle blower protections, but if ethics were easy, people wouldn't have to talk about them so much.