One interesting aspect of this story is that in many other jurisdictions, Alvarez's conduct could be argued to be a violation of the rules of professional conduct. Model Rule 3.8 includes the following two sections:
(g) When a prosecutor knows of new, credible and material evidence creating a reasonable likelihood that a convicted defendant did not commit an offense of which the defendant was convicted, the prosecutor shall: (1) promptly disclose that evidence to an appropriate court or authority, and (2) if the conviction was obtained in the prosecutor’s jurisdiction, (i) promptly disclose that evidence to the defendant unless a court authorizes delay, and (ii) undertake further investigation, or make reasonable efforts to cause an investigation, to determine whether the defendant was convicted of an offense that the defendant did not commit.Of course, if these sections applied, the question would be whether the investigation constitutes "new evidence." Alvarez has argued it does not.
(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.
But the question in Illinois is different because these sections were not adopted in Illinois when the state adopted the Model Rules in 2010. In the end, right now it appears the decision does not depend on anything other than Alvarez's discretion.
Slate has the story here.